arm, config: Add initial support for Ruby

arm, config: Add initial support for Ruby

Add initial support for creating an ARM system with a Ruby-based
memory system. This support is currently experimental and limited to
the new VExpress_GEM5_V1 platform.

Change-Id: I36baeb68b0d891e34ea46aafe17b5e55217b4bfa
Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Brad Beckmann <brad.beckmann@amd.com>