ARM: dts: vf-colibri-eval-v3: Use enable-gpios for BL_ON

Use pwm-backlight driver 'enable-gpios' property for backlight on/off
control.

Signed-off-by: Bhuvanchandra DV <bhuvanchandra.dv@toradex.com>
Acked-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>