arch-arm: Check cache maintenance insts for permission faults

arch-arm: Check cache maintenance insts for permission faults

In AArch32, data cache maintenance instructions that operate by VA do
not generate permission faults.

In AArch64, a data cache invalidate instruction can generate a
permission fault when there are no write permissions to the specified
VA. Data cache clean and data cache clean and invalidate instructions
do not generate permission faults.

Checks for external aborts are also bypassed for data cache
maintenance instructions.

Change-Id: Iea5bc665e4cf66d528e36b671535b66637c4b224
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/7827
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>