dt-bindings: leds: Convert register-bit-led binding to DT schema

Convert the register-bit-led binding to DT schema format.

As the example just repeats nearly identical nodes, trim it down to a
few nodes and use some documented values for 'linux,default-trigger'.

Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Pavel Machek <pavel@ucw.cz>
Cc: linux-leds@vger.kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20210913192816.1225025-2-robh@kernel.org


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