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: Ibbc8c9499a32e63fd0957a6e254608fbf6fa90c9
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>