fbdev: msm: update fb_release sequence

Calling mdss_fb_pan_display from mdss_fb_release path can
result in commit cnt getting incremented resulting in UI freeze
issues due to difference between commit_cnt and release fence
count. To avoid this scenario, release the mdss overlay when
fb ref cnt is zero or there is a device shutdown.

Change-Id: Ibb6de7c712bda631ad9c9180af243661f3d51764
Signed-off-by: Nirmal Abraham <nabrah@codeaurora.org>