feat(plat/arm/sgi): Enable support to read pcie data from sds

To enable the support of dynamic PCIe region calculation, SCP
calculates and programs the region information in SDS.
The UEFI consumes this information and then updates the ACPI table
accordingly.

This patch enables the support to read the data from SDS and then
program it into FDT for UEFI to consume.

Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Change-Id: If11b526bc2e76a547e9b9507957acc5c84a40810