Now that the use of 18 registers for FF-A is supported. Registers
from x0-x17 can be used by FF-A to return call results. StMM also uses
registers x19-x23 to store SPMC boot information.
Use the x24 register to store the stack address instead of x12
to avoid it being clobbered by FF-A calls.
Signed-off-by: Mohamed Gamal Morsy <mohamed.morsy@arm.com>
e0852f75d8