plat/rdremont: SRAM GPT mapping and L1GPT BL2 MMAP

In order to enable the BL1->BL2 bootflow:
- move the ARM_MAP_GPT_L1_DRAM
  MMU region mapping from BL31 to BL2 as GPT setup is handled by BL2.
- remove ARM_MAP_L0_GPT_REGION MMU region mapping from BL31 as it is
  handled by BL2.
- bump the L1 GPT size
- Remove ARM_PAS_EL3_DRAM as all BLs including BL31 will be running from
  SRAM.
- add ARM_PAS_BL_RAM to GPT mapping since the BL1, BL2 will be placed in
  this region.

Signed-off-by: Sathyam Panda <sathyam.panda@arm.com>
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>