arch-arm: AddressSize check on translateMmuOff for AArch64 only

arch-arm: AddressSize check on translateMmuOff for AArch64 only

Motivation:
An AddressSizeFault on AArch32 can only happen during a table walk
since the register used as a base by LD/ST is always 32 bit wide.
On AArch64 on the other hand, addresses can be 64bit wide;
when MMU is off (no virtual memory) an invalid physical address
can be specified

Change-Id: Id3ef170e99202c6b0b511fa7205c754956861720
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/31274
Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>