arch, arm: Effect of AT instructions on descriptor handling

arch, arm: Effect of AT instructions on descriptor handling

Some address translation instructions will stop translation after
the 1st stage and intercept the IPA, even in the presence of
stage 2 (eg AT S1E1).  However, in the case of a TLB miss, the
table descriptors still need to be translated from IPA to PA to
avoid fetching the wrong addresses.  This commit splits whether
IPA->PA translation is required for the VA and/or for the table
descriptors.

Change-Id: Ie53cdc00585f116150256f1d833460931b3bfb7d
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/13781
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>