Platform/Sgi: Add Ssdt and Mcfg tables for RD-N2

RD-N2 platform is updated to have five PCIe segments with 32 buses
under each segments. So add new Ssdt and Mcfg tables specific to RD-N2
platform with five segments each with different ECAM base addresses and
MMIO addresses.

Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Change-Id: I2f606f1dd22e40e4a9781a49abaa5a1c8a6cec8b