drm/msm/sde: fix race condition between sde irq free and irq callback

In the current implementation there can be a race condition
where sde irq callback table is being freed and at the same
time corresponding irq might get triggered. This will cause
invalid memory access. Fix this by making irq callback table
free and callback trigger mutually exclusive.

Change-Id: Id8bd87e0e53f3d8bf4ba8f7dbbdaa19b9df29422
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>