drm/msm: Use idr_preload()

Avoid allocation under idr_lock, to prevent deadlock against the
job_free() path (which runs on same thread as job_run(), which makes
it also part of the fence-signaling path.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/527847/
Link: https://lore.kernel.org/r/20230320144356.803762-12-robdclark@gmail.com