Let's report IO-coherent access is supported for translation
table walks, descriptor fetches and queues by setting the COHACC
override flag. Without that, we observe wrong command opcodes.
The DT description also advertises the dma coherency.

Fixes a703b4f6 ("hw/arm/virt-acpi-build: Add smmuv3 node in IORT table")
Signed-off-by: NEric Auger <eric.auger@redhat.com>
Reported-by: NShameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
Tested-by: NShameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Reviewed-by: NAndrew Jones <drjones@redhat.com>
Message-id: 20190107101041.765-1-eric.auger@redhat.com
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>