of: property: fw_devlink: Add support for "leds" and "backlight"

Allows tracking dependencies between leds/backlights devices and their
consumers.

Signed-off-by: Saravana Kannan <saravanak@google.com>
Link: https://lore.kernel.org/r/20210814023132.2729731-2-saravanak@google.com


Signed-off-by: Rob Herring <robh@kernel.org>