IntelFsp2Pkg: Support FSP private temporary memory.

IntelFsp2Pkg: Support FSP private temporary memory.

REF:https://bugzilla.tianocore.org/show_bug.cgi?id=3153

In FSP the temporary memory provided by bootloader typically will be
totally given to PeiCore as Heap, but in some cases FSP may have to
reserve some more temporary memory for private usage.

This commit adds this flexibility for FSP to reserve some
temporary memory before giving them to PeiCore.

Cc: Maurice Ma <maurice.ma@intel.com>
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: Nate DeSimone <nathaniel.l.desimone@intel.com>
Reviewed-by: Star Zeng <star.zeng@intel.com>