ARM: dts: imx6q-apalis-ixora: Remove use of pwm-leds

Remove use of pwm-leds and use the standard /sys/class/pwm
interface from PWM subsystem.

Signed-off-by: Sanchayan Maity <maitysanchayan@gmail.com>
Acked-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>