MIPS: ath79: add common GPIO buttons device

Almost all boards have one or more push buttons connected to GPIO lines.
This patch adds common code to register a platform_device for them.

The patch also adds support for the buttons on the PB44 board.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Imre Kaloz <kaloz@openwrt.org>
Cc: linux-mips@linux-mips.org
Cc: Luis R. Rodriguez <lrodriguez@atheros.com>
Cc: Cliff Holden <Cliff.Holden@Atheros.com>
Cc: Kathy Giori <Kathy.Giori@Atheros.com>
Patchwork: https://patchwork.linux-mips.org/patch/1954/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/ath79/dev-gpio-buttons.h

@@ -0,0 +1,23 @@
+/*
+ *  Atheros AR71XX/AR724X/AR913X GPIO button support
+ *
+ *  Copyright (C) 2008-2010 Gabor Juhos <juhosg@openwrt.org>
+ *  Copyright (C) 2008 Imre Kaloz <kaloz@openwrt.org>
+ *
+ *  This program is free software; you can redistribute it and/or modify it
+ *  under the terms of the GNU General Public License version 2 as published
+ *  by the Free Software Foundation.
+ */
+
+#ifndef _ATH79_DEV_GPIO_BUTTONS_H
+#define _ATH79_DEV_GPIO_BUTTONS_H
+
+#include <linux/input.h>
+#include <linux/gpio_keys.h>
+
+void ath79_register_gpio_keys_polled(int id,
+				     unsigned poll_interval,
+				     unsigned nbuttons,
+				     struct gpio_keys_button *buttons);
+
+#endif /* _ATH79_DEV_GPIO_BUTTONS_H */