configs/infra: enable EL3_EXCEPTION_HANDLING when SPM is enabled

The flag EL3_EXCEPTION_HANDLING must be enabled to compile trusted
firmware with secure partion support. So allow this flag to the enabled
even if RAS_EXTENSION is not enabled for the platform.

Signed-off-by: Omkar Anand Kulkarni <omkar.kulkarni@arm.com>
Change-Id: I0dc9abae89c65f9616a023c17f55324a336407fe