drm/msm: skip re-emitting IBs for unusable VMs

When a VM is marked as an usuable we disallow new submissions from it,
however submissions that where already scheduled on the ring would still
be re-sent.

Since this can lead to further hangs, avoid emitting the actual IBs.

Fixes: 6a4d287a ("drm/msm: Mark VM as unusable on GPU hangs")
Signed-off-by: Antonino Maniscalco <antomani103@gmail.com>
Reviewed-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/668314/


Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>