refactor(ast2700): update memory layout

Update the memory layout for both BL31 and BL32 FW based on
the 1GB DRAM space of the AST2700 EVB.

Minor:
 - Use SZ_xx macro to define size for better readability

Signed-off-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>
Change-Id: I6d8285bd675321f615bb67cdd27bb4b6cb4c8b16
1 file changed