x86: pcengines apuv2 gpio/leds/keys platform driver

Driver for PCengines APUv2 board's front LEDs and Button,
which are attached to AMD PCH GPIOs. Due to lack of dedicated
ACPI entry, detecting the board via DMI.

Cc: linux-gpio@vger.kernel.org
Cc: linus.walleij@linaro.org
Cc: bgolaszewski@baylibre.com
Cc: dvhart@infradead.org
Cc: platform-driver-x86@vger.kernel.org
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>