msm: vidc: flush queued work during device suspend

This change flushes any queued work related to power collapse,
once the device is power suspended.
There are applications which do not destroy video instance
on suspending the device. For such applications, if the device
is power suspended, video driver does not prepare venus for
power collapse.
Considerable power saving is observed by power collapsing
venus before the device goes in suspend state.

Change-Id: I11252e45b10d0d3d3eefb38994acd083c847bbb8
Signed-off-by: Vikash Garodia <vgarodia@codeaurora.org>