ARM: dts: msm: Refine PWM frequency for 8909 SKUT backlight change

PWM frequency should be 31K for panel fl10802 in 8909 SKUT. Change
the device tree file for the frequency to enable backlight change.
And remove backlight enable command in panel initialize commands
to avoid white screen when device resume.

Change-Id: I1a8eab7729c7d9acd6dfa716c1b97ecc6f7516ca
Signed-off-by: Yang Xu <yangxu@codeaurora.org>