pcengines/apu1: Add ACPI led, button and GPIO devices.

pcengines/apu1: Add ACPI led, button and GPIO devices.

Provide ACPI devices with devicetree-compatible annotations for the
three leds and the button of the APU1, as well as the GPIO driver.

This will cause the Linux kernel to automatically load the following
modules:
  leds_gpio (CONFIG_LEDS_GPIO)
  gpio_keys_polled (CONFIG_KEYBOARD_GPIO_POLLED)
  gpio_sb8xx (CONFIG_GPIO_SB8XX)

See
http://events.linuxfoundation.org/sites/events/files/slides/ACPI_vs_DT.pdf
and https://lwn.net/Articles/612062/ for some more information on how
the PRP0001 HID works.

To make this usable a Linux GPIO driver for the AMD chipset is also
required, which I am currently working on, but have not submitted
upstream yet.

Leds have been named after the convention in
Documentation/leds/leds-class.txt:
LED Device Naming
=================
Is currently of the form:
"devicename:colour:function"

For comparison, on an OpenWRT device:
GPIOs 0-21, ath79:
 gpio-1   (tp-link:green:usb   ) out hi
 gpio-2   (tp-link:green:system) out lo
 gpio-3   (reset               ) in  hi
 gpio-5   (tp-link:green:qss   ) out lo
 gpio-7   (qss                 ) in  hi
 gpio-9   (tp-link:green:wlan  ) out lo
 gpio-18  (rtl8366rb           ) in  hi
 gpio-19  (rtl8366rb           ) in  hi

On the apu1:
GPIOs 288-511, platform/PRP0001:00, AMD SB8XX/SB9XX/A5X/A8X GPIO driver:
 gpio-475 (switch1             ) in  hi
 gpio-477 (apu1:green:led1     ) out hi
 gpio-478 (apu1:green:led2     ) out hi
 gpio-479 (apu1:green:led3     ) out hi

Change-Id: I956ee92d9d98ef27a83ccb30d314543bd8634f2c
Signed-off-by: Tobias Diedrich <ranma+coreboot@tdiedrich.de>
Reviewed-on: http://review.coreboot.org/10540
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>