Platform/Sgi: add remote memory descriptor

8GB address region starting at 0x3FE00000000 is reserved for extended
Remote Memory use. One of the use case, for extended remote memory
region, is using it as CXL.Mem region.

Remote memory region, with Normal memory attributes, is included into
the Translation table entries based on the PcdRemoteCxlMemory flag
status.

Resource descriptor for Remote CXL device memory is not created in
PlatformLibMem, it will be added at later execution phase after the
discovery of CXL Mem device.

This patch adds a Pcd, PcdRemoteCxlMemory for identifying a platform
with CXL enabled configuration.

Also marked Local memory block count, for creating SRAT tables in
subsequent patch.

Signed-off-by: Sayanta Pattanayak <sayanta.pattanayak@arm.com>
Change-Id: I8c16b71fcece70f5720203c4c0a0b5f7e51a41ca