IntelFsp2WrapperPkg: Perform post FSP-S process.

IntelFsp2WrapperPkg: Perform post FSP-S process.

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=1716

In API mode FSP wrapper will perform some post
FSP-S process but such process was skipped in Dispatch
mode which may impact some of the boot loaders.
To align behavior between API and Dispatch, an
End-of-Pei callback is introduced to perform same process
in Dispatch mode.

Note: If boot loader implemented its own
      PostFspsHobProcess (), it has to check
      PcdFspModeSelection and support each mode
      properly.

Test: Verified on internal platform and both
      FSP API and Dispatch modes booted successfully.

Cc: Nate DeSimone <nathaniel.l.desimone@intel.com>
Cc: Star Zeng <star.zeng@intel.com>
Signed-off-by: Chasel Chiu <chasel.chiu@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>
Reviewed-by: Nate DeSimone <nathaniel.l.desimone@intel.com>