arm: Add support for the mcr dc{ic,i,c}mvac, dccmvau instructions

arm: Add support for the mcr dc{ic,i,c}mvac, dccmvau instructions

This patch adds support for the ARMv7 cache maintenance
intructions:
* mcr dccmvac cleans a VA to the PoC
* mcr dcimvac invalidates a VA to the PoC
* mcr dccimvac cleans and invalidates a VA to the PoC
* mcr dccmvau cleans a VA to the PoU

Change-Id: I6511f203039ca145cc9128ddf61d09d6d7e40c10
Reviewed-by: Stephan Diestelhorst <stephan.diestelhorst@arm.com>
Reviewed-by: Anouk Van Laer <anouk.vanlaer@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/5059
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>