feat: introduce test to generate SError

Introduce capability to generate SError in TFTF.
One of the usecases of this capability is to test EL3 feature of
trapping lower ELs SError.

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: I4bc78edf21f9329f1ed76b0ae27db223a83a9670
3 files changed