drm/ttm: make ttm reservation calls behave like reservation calls

drm/ttm: make ttm reservation calls behave like reservation calls

This commit converts the source of the val_seq counter to
the ww_mutex api. The reservation objects are converted later,
because there is still a lockdep splat in nouveau that has to
resolved first.

Signed-off-by: Maarten Lankhorst <[email protected]>
Reviewed-by: Jerome Glisse <[email protected]>
Signed-off-by: Dave Airlie <[email protected]>