FVP: In BL31/SP_MIN, map only the needed DRAM region statically

FVP: In BL31/SP_MIN, map only the needed DRAM region statically

Rather than creating entry in plat_arm_mmap array to map the
entire DRAM region in BL31/SP_MIN, only map a smaller region holding
HW_CONFIG DTB. Consequently, an increase in number of sub-translation
tables(level-2 and level-3) i.e., MAX_XLAT_TABLES is necessary to map
the new region in memory.

In order to accommodate the increased code size in BL31 i.e.,
PROGBITS, the max size of BL31 image is increased by 0x1000(4K).

Change-Id: I540b8ee550588e22a3a9fb218183d2ab8061c851
Signed-off-by: Madhukar Pappireddy <madhukar.pappireddy@arm.com>