arch-arm: Use ExceptionLevel type in TlbEntry

arch-arm: Use ExceptionLevel type in TlbEntry

Replacing uint8_t with ExceptionLevel type in the arm TlbEntry. The
variable is representing the translation regime it is targeting.

Change-Id: Ifcd6e86c5d73f752e8476a2b7fda9ea74a0c7a3b
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/19488
Reviewed-by: Ciro Santilli <ciro.santilli@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>