MLK-11571 [MX7D-12LPDDR3] LCD: Screen still shows with weak backlight after...

MLK-11571 [MX7D-12LPDDR3] LCD: Screen still shows with weak backlight after system entered suspend mode. 100%

The 'backlight' and 'pwm1' are disabled due to the lpsr mode
not ready in the previous patch in the imx7d-12x12-lpddr3-arm2
dts. So they should be enabled again after lpsr ready.

Signed-off-by: Fancy Fang <chen.fang@freescale.com>