drm/msm: Take lru lock once per submit_pin_objects()

Split out pin_count incrementing and lru updating into a separate loop
so we can take the lru lock only once for all objs.  Since we are still
holding the obj lock, it is safe to split this up.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Patchwork: https://patchwork.freedesktop.org/patch/551025/