drm/msm: Move cmdstream dumping out of sched kthread

This is something that can block for arbitrary amounts of time as
userspace consumes from the FIFO.  So we don't really want this to
be in the fence signaling path.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/532617/