drm/msm: Take single rpm refcount on behalf of all submits

Instead of separate refcount for each submit, take single rpm refcount
on behalf of all the submits. This makes it easier to drop the rpm
refcount during recovery in an upcoming patch.

Signed-off-by: Akhil P Oommen <quic_akhilpo@quicinc.com>
Patchwork: https://patchwork.freedesktop.org/patch/498392/
Link: https://lore.kernel.org/r/20220819015030.v5.2.Ifee853f6d8217a0fdacc459092bbc9e81a8a7ac7@changeid
Signed-off-by: Rob Clark <robdclark@chromium.org>