Platform: Adjust required RAM size for SPE in MUSCA_A

This patch adjusts the required RAM size for the SPE
in a MUSCA_A target to meet the worst case scenario
which is 96 KB for SPE. The remaining 32 KB are
reserved for the NSPE.

Change-Id: Iadc72cc40b084cffd09f4461f6d088a4fdefaf31
Signed-off-by: Antonio de Angelis <antonio.deangelis@arm.com>