Enabling EFI_PEI_FIRMWARE_VOLUME_PPI introduced by PI1.2.

Enabling EFI_PEI_FIRMWARE_VOLUME_PPI introduced by PI1.2.
1, Implement EFI_PEI_FIRMWARE_VOLUME_PPI for FFS2 format as build-in supporting FV format in PeiCore.
2, Reduce the assumption of memory-mapped FV in PeiCore. PeiCore should access FV via EFI_PEI_FIRMWARE_VOLUME_PPI interface but not cast FvHandle/FileHandle to EFI_FIRMWARE_VOLUME_HEADER/EFI_FV_FILE_HEADER directly.
3, Reduce AllFv[] and AllFvCount in PEI_CORE_INSTANCE structure. Original PEI_CORE_INSTANCE use AllFv[] and Fv[] array to manage discovered FV and dispatched FV. But not need to make thing too complex. Now PEI_CORE_FV_HANDLE array of Fv[] will take responsibility to manage all FV instance and status.
4, Fix the bug use PeiDispatcher use wrong index for PeiFfsFindNextVolume(),
5, Fix the bug in PeiFfsFindNextVolume(), if instance is not found, *VolumeHandle should be set to NULL but not VolumeHandle was set to NULL.

git-svn-id: https://edk2.svn.sourceforge.net/svnroot/edk2/trunk/edk2@9407 6f19259b-4bc3-4df7-8a09-765794883524