arch-arm: Fix atomics permission checks in TLB
arch-arm: Fix atomics permission checks in TLB

For stage 2 translations, atomic accesses were not checking the
access permission bits in the page table descriptors, and were
instead wrongly using the nature of the request itself
(r/w booleans).

Cherry-picked from:
https://gem5-review.googlesource.com/c/public/gem5/+/42073

Change-Id: I919a08b690287b03426d9124a61887e521f47823
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/43143
Reviewed-by: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Maintainer: Jason Lowe-Power <92de577f37050ad05b60626d2f17913f40dcb1a2@gmail.com>
Tested-by: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>

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