SDEI: Assert that dynamic events have Normal priority
SDEI: Assert that dynamic events have Normal priority

The SDEI specification requires that binding a client interrupt
dispatches SDEI Normal priority event. This means that dynamic events
can't have Critical priority. Add asserts for this.

Change-Id: I0bdd9e0e642fb2b61810cb9f4cbfbd35bba521d1
Signed-off-by: Jeenu Viswambharan <5b289de972918ffd274229d00560f010009baf9e@arm.com>

lsigithub/arm-trusted-firmware_public,achingupta/arm-trusted-firmware,lsigithub/arm-trusted-firmware_public,achingupta/arm-trusted-firmware