arch-arm: Annotate CM flag in AA64 CM Instructions

arch-arm: Annotate CM flag in AA64 CM Instructions

DC ZVA instruction is not classified as a cache maintenance instruction,
and therefore its execution cannot cause this field to be set to 1.

Change-Id: I0f30db1e6fc629dc52293edfb2bac4cf99ee49cc
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/+/21306
Tested-by: kokoro <noreply+kokoro@google.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>