The bl_en_pin GPIO pinmux is configured as "gpio_in", which makes it
conflicts with the real GPIO usage (out), and makes the backlight not
usable.

Drop the GPIO pinmux for it, thus this GPIO can be correctly used.
Signed-off-by: Icenowy Zheng <icenowy@aosc.xyz>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>