drm/msm/sde: modify RM to commit hw in check_only phase

SDE RM is modified to maintain hw allocation as part of
atomic_check_only phase. It ensures that if a topology is
checked and supported, the hw is maintained in a staging
state between check_only and commit phase. Cleanup for
validate is called as part of crtc destroy state.

Change-Id: I13c38bd689583ce316b43e827cb76f16e744adad
Signed-off-by: Nilaan Gunabalachandran <ngunabal@codeaurora.org>