SPM: Use the saved EXC_RETURN payload When returning to the ISR

Save the EXC_RETURN payload into the stack when the deprivileged
FLIH SVC is called. When FLIH function returns, use the saved
EXC_RETURN payload to return to ISR.

Signed-off-by: Chendi Sun <chendi.sun@arm.com>
Change-Id: I1b3a1596903cae0920f9f64be1cdaf6d9a12df99
5 files changed