gpu: host1x: Do not setup DMA for virtual devices

The host1x devices are virtual compound devices and do not perform DMA
accesses themselves, so they do not need to be set up for DMA.

Ideally we would also not need to set up DMA masks for the virtual
devices, but we currently still need those for legacy support on old
hardware.

Tested-by: Jon Hunter <jonathanh@nvidia.com>
Acked-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240314154943.2487549-1-thierry.reding@gmail.com