fix(morello): move BL31 to run from DRAM space

The EL3 runtime firmware has been running from internal trusted
SRAM space on the Morello platform. Due to unavailability of tag
support for the internal trusted SRAM this becomes a problem if
we enable capability pointers in BL31.

To support capability pointers in BL31 it has to be run from the
main DDR memory space. This patch updates the Morello platform
configuration such that BL31 is loaded and run from DDR space.

Signed-off-by: Manoj Kumar <manoj.kumar3@arm.com>
Change-Id: I16d4d757fb6f58c364f5133236d50fc06845e0b4