Platform/Sgi: autogenerate SoC expansion block iort table data

Add support to the IORT table generator to generate the IORT nodes
for SoC expansion block that is connected to the IO virtualization
block on RD platforms.
Each instance of the SoC expansion block contains 1 each of SMMUv3
and GIC-ITS, and two PL330 DMA devices.

Signed-off-by: Nishant Sharma <nishant.sharma@arm.com>
Signed-off-by: Vivek Gautam <vivek.gautam@arm.com>
Change-Id: I3ec955dcc303718a80e4ecbe3ea9673e947d1ae4