gpu: host1x: Enable system suspend callbacks

With the previous CDMA stop fix, executing runtime PM ops around
system suspend now makes channel submissions work after system
suspend, so do that.

Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230901111510.663401-3-cyndis@kapsi.fi