OvmfPkg: implement LockBoxLib

OvmfPkg: implement LockBoxLib

The S3 suspend/resume infrastructure depends on the LockBox library class.
The edk2 tree currently contains Null and SMM instances. The Null instance
is useless, and the SMM instance would require SMM emulation by including
the SMM core and adding several new drivers, which is deemed too complex.

Hence add a simple LockBoxLib instance for OVMF.

jordan.l.justen@intel.com:
 * use PCDs instead of EmuNvramLib
   - clear memory in PlatformPei on non S3 boots
 * allocate NVS memory and store a pointer to that memory
   - reduces memory use at fixed locations

Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
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@15301 6f19259b-4bc3-4df7-8a09-765794883524