opteed: assume aarch64 for optee
opteed: assume aarch64 for optee

OPTEE to execute in aarch64 bit mode, set it accordingly
when execution transitions from EL3 to EL1

Change-Id: I59f2f940bdc1aac10543045b006a137d107ec95f
Signed-off-by: Ashutosh Singh <c92cd32d7af0588e5b77f1393a78110e86eb7d9b@arm.com>

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