OvmfPkg/PlatformPei: rebase and resize the permanent PEI memory for S3

OvmfPkg/PlatformPei: rebase and resize the permanent PEI memory for S3

Move the permanent PEI memory for the S3 resume boot path to the top of
the low RAM (just below TSEG if the SMM driver stack is included in the
build). The new size is derived from CpuMpPei's approximate memory demand.

Save the base address and the size in new global variables, regardless of
the boot path. On the normal boot path, use these variables for covering
the area with EfiACPIMemoryNVS type memory.

PcdS3AcpiReservedMemoryBase and PcdS3AcpiReservedMemorySize become unused
in PlatformPei; remove them.

Cc: Jeff Fan <jeff.fan@intel.com>
Cc: Jordan Justen <jordan.l.justen@intel.com>
Cc: Michael Kinney <michael.d.kinney@intel.com>
Contributed-under: TianoCore Contribution Agreement 1.0
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Jeff Fan <jeff.fan@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>