feat: test to verify SError reflected back to lower EL from EL3

Tests introduced to verify
  - reflection of errors back to lower EL from EL3 in KFH mode
  - Nested handling of exception in case of FFH mode

Signed-off-by: Manish Pandey <manish.pandey2@arm.com>
Change-Id: Ie9f4b911a65672dcb0dd1673b376872fbe885c24
8 files changed