arm: v7R: Add support for enabling caches

Cache maintenance procedure is same for v7A and v7R
processors. So re-use cache-cp15.c file except for
mmu parts.

Tested-by: Michal Simek <michal.simek@xilinx.com>
Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>