Platform/Sgi: Update 64-bit Pci Mmio base and size

Platforms which uses SgiMemoryMap.dsc.inc has been updated to use
0x5_0000_0000 as base for the 64-bit Pci MMIO region and the size has
been limited to 4GiB. Update SgiMemoryMap.dsc.inc so that the OS would
use correct 64-bit Pci MMIO region.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I0a473eccef3d4c2e67dae87206331bcf6cca582d