leds: trigger: Load trigger modules on-demand if used as default trigger

leds: trigger: Load trigger modules on-demand if used as default trigger

Even if a trigger is set as default trigger for a LED device,
the respective trigger module (if built as module) isn't automatically
loaded by the kernel if the LED device is registered. I think we can
do better. Try to load the module asynchronously by alias
ledtrig:<trigger name>. This requires that such an alias is added to
relevant triggers.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/79adb260-06ad-443a-a68e-abe4498c3298@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>