dev-arm: SMMUv3, single interconnect attachment

dev-arm: SMMUv3, single interconnect attachment

The attachment (port binding) of the SMMUv3 master and control
ports is independent of the connection of device masters to it.

This behaviour is now moved from SMMUv3::connect to
RealView::attachSmmu, as it is a responsibility of the Platform
designer.

This fixes crashes when connecting multiple device masters.

Change-Id: If1e8f55d51876fe761f881e3044ffec637c21b09
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/26923
Maintainer: Giacomo Travaglini <giacomo.travaglini@arm.com>
Tested-by: Gem5 Cloud Project GCB service account <345032938727@cloudbuild.gserviceaccount.com>