rdv3r1: add model startup support for RD-V3-R1 platform

Added initial model startup support for RD-V3-R1 platform.
The RD-V3-R1 platform is the dual chiplets platforms.
Added support for uefi, busybox, buildroot tests.

RD-V3-R1 now have PCIe enabled. PCIe is needed to enable distro boot.
Added the RD-V3-R1 to the disto boot supported platforms in the config.

Signed-off-by: Joel Goddard <Joel.Goddard@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>
Signed-off-by: Lokesh B V <Lokesh.BV@Arm.com>
Change-Id: I77956d6945706ac588bb17023947f2fe43c58167