This commit adds very basic support for device tree probing. Currently,
only a PWM and a list of distinct brightness levels can be specified.
Enabling or disabling backlight power via GPIOs is not yet supported.
Reviewed-by: NShawn Guo <shawn.guo@linaro.org>
Reviewed-by: NMark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: NThierry Reding <thierry.reding@avionic-design.de>