msm_fb: Set backlight during resume after first display commit

Set the backlight after resume only after the first display
commit is done. This will avoid panel specific transients to
show up on the panel during its initialization. Also, avoid
backlight scaling during resume until backlight is set.

CRs-fixed: 468633
Change-Id: Ic9e24e9cd9d57fbdd767f9dae92f418b0b139c94
Signed-off-by: Padmanabhan Komanduru <pkomandu@codeaurora.org>