leds: triggers: Add helper led_match_default_trigger

Avoid code duplication and factor out common functionality to new
helper led_match_default_trigger().

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Link: https://lore.kernel.org/r/d78eef6f-c18c-4546-b83e-6d1890849154@gmail.com


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