msm_fb: display: change the location of wakeup timer call

There are two pathes (pan display and overlay commit) to commit
display buffer, so change the location of cpu timer wakup call to the
common pipe_commit function to make sure cpu get waked up around
vsync.

Signed-off-by: Huaibin Yang <huaibiny@codeaurora.org>
Change-Id: Idbe6049d740a7e17a6a90e28566f7a9c74e348f2