Fix build for SEPARATE_CODE_AND_RODATA=0

Fix build for SEPARATE_CODE_AND_RODATA=0

TF won't build since no memory region is specified
for when SEPARATE_CODE_AND_RODATA=0 it still relies on
the ARM_MAP_BL_RO_DATA region which is never defined for
this case. Create memory region combining code and RO data for
when the build flag SEPARATE_CODE_AND_RODATA=0 to fix this

Change-Id: I6c129eb0833497710cce55e76b8908ce03e0a638
Signed-off-by: Daniel Boulby <daniel.boulby@arm.com>