OvmfPkg: PlatformPei: detect S3 Resume in CMOS and set boot mode accordingly

OvmfPkg: PlatformPei: detect S3 Resume in CMOS and set boot mode accordingly

Data is transferred between S3 Suspend and S3 Resume as follows:

S3 Suspend (DXE):

(1) BdsLibBootViaBootOption()
      EFI_ACPI_S3_SAVE_PROTOCOL [AcpiS3SaveDxe]
      - saves ACPI S3 Context to LockBox  ---------------------+
        (including FACS address -- FACS ACPI table             |
        contains OS waking vector)                             |
                                                               |
      - prepares boot script:                                  |
        EFI_S3_SAVE_STATE_PROTOCOL.Write() [S3SaveStateDxe]    |
          S3BootScriptLib [PiDxeS3BootScriptLib]               |
          - opcodes & arguments are saved in NVS.  --+         |
                                                     |         |
      - issues a notification by installing          |         |
        EFI_DXE_SMM_READY_TO_LOCK_PROTOCOL           |         |
                                                     |         |
(2) EFI_S3_SAVE_STATE_PROTOCOL [S3SaveStateDxe]      |         |
      S3BootScriptLib [PiDxeS3BootScriptLib]         |         |
      - closes script with special opcode  <---------+         |
      - script is available in non-volatile memory             |
        via PcdS3BootScriptTablePrivateDataPtr  --+            |
                                                  |            |
    BootScriptExecutorDxe                         |            |
      S3BootScriptLib [PiDxeS3BootScriptLib]      |            |
      - Knows about boot script location by  <----+            |
        synchronizing with the other library                   |
        instance via                                           |
        PcdS3BootScriptTablePrivateDataPtr.                    |
      - Copies relocated image of itself to                    |
        reserved memory. --------------------------------+     |
      - Saved image contains pointer to boot script.  ---|--+  |
                                                         |  |  |
Runtime:                                                 |  |  |
                                                         |  |  |
(3) OS is booted, writes OS waking vector to FACS,       |  |  |
    suspends machine                                     |  |  |
                                                         |  |  |
S3 Resume (PEI):                                         |  |  |
                                                         |  |  |
(4) PlatformPei sets S3 Boot Mode based on CMOS          |  |  |
                                                         |  |  |
(5) DXE core is skipped and EFI_PEI_S3_RESUME2 is        |  |  |
    called as last step of PEI                           |  |  |
                                                         |  |  |
(6) S3Resume2Pei retrieves from LockBox:                 |  |  |
    - ACPI S3 Context (path to FACS)  <------------------|--|--+
                                      |                  |  |
                                      +------------------|--|--+
    - Boot Script Executor Image  <----------------------+  |  |
                                                            |  |
(7) BootScriptExecutorDxe                                   |  |
      S3BootScriptLib [PiDxeS3BootScriptLib]                |  |
      - executes boot script  <-----------------------------+  |
                                                               |
(8) OS waking vector available from ACPI S3 Context / FACS  <--+
    is called

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
[jordan.l.justen@intel.com: move code into BootModeInitialization]
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Laszlo Ersek <lersek@redhat.com>
git-svn-id: https://svn.code.sf.net/p/edk2/code/trunk/edk2@15290 6f19259b-4bc3-4df7-8a09-765794883524