gpu: host1x: Stop CDMA before suspending

Before going into suspend, wait all CDMA to go idle and stop it.
This will ensure no channel is still active while we enter
suspend, and ensures the driver doesn't think that CDMA is still
active when coming back from suspend (as HW state has been reset).

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901111510.663401-2-cyndis@kapsi.fi