MLK-11514 [MX6SX] No GUI show and the display is blank after bootup to x rootfs with...

MLK-11514 [MX6SX] No GUI show and the display is blank after bootup to x rootfs with LVDS.100%.

The reason for this issue is that, on imx6sx platform, there is a display mix
to control the display modules(including lcdif) power on/off. When the fb
driver calls the 'pm_runtime_put_sync_suspend()', the display mix will be
powered down. And at this moment, all the register settings for lcdif always
have no effects. So the pm_runtime calling points in mxsfb driver should be
optimized to avoid this kind of cases.

Signed-off-by: Fancy Fang <chen.fang@freescale.com>
(cherry picked from commit 3b85eb989c89fb1c6d08215e435d72ab175e4e1e)

Conflicts:
	drivers/video/mxsfb.c