ARM: dts: cm-t335: add support for PWM backlight

Add pinmux configuration for ECAP0 pin.
Add node for PWM backlight device.
Use PWM output from ecap0 as backlight source.

Signed-off-by: Ilya Ledvich <ilya@compulab.co.il>
Signed-off-by: Uri Mashiach <uri.mashiach@compulab.co.il>
Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Tony Lindgren <tony@atomide.com>