fbtft gpio backlight

[qianfan <qianfanguijin@xxxxxxx>]

Hi:

fbtft_register_backlight assume backlight is off, get polarity from 
current state of pin. but the led gpio is requested by GPIOD_OUT_LOW 
flag, which means the gpio state when fbtft_register_backlight is always 
low.

Is it a bug?

Thanks