leds: Replace {devm_}led_classdev_register() macros with inlines

Replace preprocessor macro aliases for legacy LED registration helpers
with inline functions. It will allow to avoid misleading compiler error
messages about missing symbol that actually wasn't explicitly used
in the code. It used to occur when CONFIG_LEDS_CLASS was undefined
and legacy (non-ext) function had been used in the code.

Signed-off-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Acked-by: Pavel Machek <pavel@ucw.cz>