backlight: lm3630a: Add firmware node support

Add fwnode support to the lm3630a driver and optionally allow
configuring the label, default brightness level, and maximum brightness
level. The two outputs can be controlled by bank A and B independently
or bank A can control both outputs.

If the platform data was not configured, then the driver defaults to
enabling both banks. This patch changes the default value to disable
both banks before parsing the firmware node so that just a single bank
can be enabled if desired. There are no in-tree users of this driver.

Driver was tested on a LG Nexus 5 (hammerhead) phone.

Signed-off-by: Brian Masney <masneyb@onstation.org>
Reviewed-by: Dan Murphy <dmurphy@ti.com>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Lee Jones <lee.jones@linaro.org>