SGI-Clark platform is the next version in the Arm's SGI platform
series. One of the primary difference between the SGI-575 platform and
the SGI-Clark platform is the MHU version (MHUv2 in case of SGI-Clark).
Add the required base support for SGI-Clark platform.

Change-Id: If396e5279fdf801d586662dad0b55195e81371e4
Signed-off-by: Chandni Cherukuri <chandni.cherukuri@arm.com>