leds: gpio: Keep driver firmware interface agnostic

The of.h is used as a proxy to mod_devicetable, replace former by
latter.

The commit 2d618014 ("leds: gpio: Configure per-LED pin control")
added yet another unneeded OF APIs. Replace with direct use of fwnode.

Altogether this makes driver agnostic to the firmware interface in use.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20231016161005.1471768-1-andriy.shevchenko@linux.intel.com


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