disp: msm: cancel all delayed_works before triggering msm_lastclose

This patch cancels all the delayed_off_works if scheduled and flushes
the display threads for completion during msm_lastclose. The commit
from msm_lastclose client modeset to disable any crtcs if enabled
is always scheduled on primary crtc_commit thread. In the current issue,
delayed_off_work is scheduled on secondary display crtc_commit thread
and primary crtc_commit thread is scheduled to turn off active crtcs
from msm_lastclose leading to null dereference access of sde_enc's
cur_master. This race is avoided by serializing the operations in
msm_lastclose.

Change-Id: I30cc95b925c8134f0064816ebe2cfdb86a49fb36
Signed-off-by: Jayaprakash Madisetty <quic_jmadiset@quicinc.com>