leds: triggers: default-on: Add module alias for module auto-loading

A bigger number of board device tree files, plus few drivers, set
default-on as default trigger for LED's. Therefore add an alias for
module auto-loading.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/7e94d26b-d772-4a07-b0f6-bb3111b9ff75@gmail.com


Signed-off-by: Lee Jones <lee@kernel.org>