Do the parsing of `linux,default-trigger` DT property to LED core.
Currently it is done in many different drivers and the code is repeated.

This patch removes the parsing from 23 drivers:
  an30259a, aw2013, bcm6328, bcm6358, cr0014114, el15203000, gpio,
  is31fl32xx, lm3532, lm36274, lm3692x, lm3697, lp50xx, lp8860, lt3593,
  max77650, mt6323, ns2, pm8058, pwm, syscon, tlc591xx and turris-omnia.

There is one driver in drivers/input which parses this property on it's
own. I shall send a separate patch there after this is applied.

There are still 8 drivers that parse this property on their own because
they do not pass the led_init_data structure to the registering
function. I will try to refactor those in the future.
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Signed-off-by: Pavel Machek <pavel@ucw.cz>