APUv2/v3 board support v4

[Enrico Weigelt, metux IT consult]

Hi folks,


this is version 4 of my APUv2/APUv3 series.

changes in v4:

 * fixed spinlocks (using own field instead of gc.bgpio_lock)
 * dropped superflous dependency on GPIO_GENERIC
 * initialize gc.base = -1
 * added Reviewed-By tags

changes in v3:

 * gpio driver
   * drop unncessary gpio id checks
   * cleanup amd_fch_gpio_set()
   * move iores outside probe()
   * shorter NULL checks and correct error in probe()
 * apu board driver
   * drop unneeded init.h
   * drop unnecessary comments
   * clean up logging
   * dont need to depend on KEYBOARD_GPIO


--mtx