In order to support SEPARATE_NOBITS_REGION for Arm platforms, we need to load
BL31 PROGBITS into secure DRAM space and BL31 NOBITS into SRAM. Hence mandate
the build to require that ARM_BL31_IN_DRAM is enabled as well.

Naturally with SEPARATE_NOBITS_REGION enabled, the BL31 initialization code
cannot be reclaimed to be used for runtime data such as secondary cpu stacks.

Memory map for BL31 NOBITS region also has to be created.

Change-Id: Ibd480f82c1dc74e9cbb54eec07d7a8fecbf25433
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>