leds: led-core: Get rid of enum led_brightness

This gets rid of enum led_brightness in the main led files,
because it is deprecated, and an unsigned int can be used instead.

We can get rid of led_brightness completely and
patches can also be supplied for the other drivers' files.

Signed-off-by: Abanoub Sameh <abanoubsameh@protonmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>