CSS: Prevent SCP_BL2/2U from overwriting BL1 RW data

CSS: Prevent SCP_BL2/2U from overwriting BL1 RW data

On ARM CSS platforms, the SCP_BL2/2U image is loaded below
BL1 read-write data. This same memory is used to load BL31
later on. But sufficient checks were not done to ensure that the
SCP_BL2 would not overwrite BL1 rw data. This patch adds the
required CASSERT checks to prevent overwrite into BL1 or BL2
memory by load of SCP_BL2/2U. Also the size of BL31 is increased
and SCP_BL2/2U size is decreased to accomodate it within the
allocated region.

Change-Id: I23b28b5e1589e91150852a06452bd52b273216ee
Signed-off-by: Soby Mathew <soby.mathew@arm.com>