OvmfPkg: Split MAINFV into a separate PEI and DXE FVs

OvmfPkg: Split MAINFV into a separate PEI and DXE FVs

By splitting the PEI and DXE phases into separate FVs,
we can only reserve the PEI FV for ACPI S3 support.
This should save about 7MB.

Unfortunately, this all has to happen in a single commit.

DEC:
* Remove PcdOvmfMemFv(Base|Size)
* Add PcdOvmfPeiMemFv(Base|Size)
* Add PcdOvmfDxeMemFv(Base|Size)

FDF:
* Add new PEIFV. Move PEI modules here.
* Remove MAINFV
* Add PEIFV and DXEFV into FVMAIN_COMPACT
   - They are added as 2 sections of a file, and compressed
     together so they should retain good compression
* PcdOvmf(Pei|Dxe)MemFv(Base|Size) are set

SEC:
* Find both the PEI and DXE FVs after decompression.
   - Copy them separately to their memory locations.

Platform PEI driver:
* Fv.c: Publish both FVs as appropriate
* MemDetect.c: PcdOvmfMemFv(Base|Size) =>
                PcdOvmfDxeMemFv(Base|Size)

OVMF.fd before:

  Non-volatile data storage
  FVMAIN_COMPACT                    uncompressed
    FV FFS file                     LZMA compressed
      MAINFV                        uncompressed
        individual PEI modules      uncompressed
        FV FFS file                 compressed with PI_NONE
          DXEFV                     uncompressed
            individual DXE modules  uncompressed
  SECFV                             uncompressed

OVMF.fd after:

  Non-volatile data storage
  FVMAIN_COMPACT                    uncompressed
    FV FFS file                     LZMA compressed
      PEIFV                         uncompressed
        individual PEI modules      uncompressed
      DXEFV                         uncompressed
        individual DXE modules      uncompressed
  SECFV                             uncompressed

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@15151 6f19259b-4bc3-4df7-8a09-765794883524