x86/platform/intel-mid: Enable GPIO keys on Merrifield

The Merrifield firmware provides 3 descriptions of buttons connected to GPIO.
Append them to the list of supported GPIO keys.
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/20170105161717.115261-1-andriy.shevchenko@linux.intel.comSigned-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/platform/intel-mid/device_libs/platform_gpio_keys.c

@@ -32,6 +32,9 @@ static struct gpio_keys_button gpio_button[] = {
 	{SW_LID,		-1, 1, "lid_switch",	EV_SW,  0, 20},
 	{KEY_VOLUMEUP,		-1, 1, "vol_up",	EV_KEY, 0, 20},
 	{KEY_VOLUMEDOWN,	-1, 1, "vol_down",	EV_KEY, 0, 20},
+	{KEY_MUTE,		-1, 1, "mute_enable",	EV_KEY, 0, 20},
+	{KEY_VOLUMEUP,		-1, 1, "volume_up",	EV_KEY, 0, 20},
+	{KEY_VOLUMEDOWN,	-1, 1, "volume_down",	EV_KEY, 0, 20},
 	{KEY_CAMERA,		-1, 1, "camera_full",	EV_KEY, 0, 20},
 	{KEY_CAMERA_FOCUS,	-1, 1, "camera_half",	EV_KEY, 0, 20},
 	{SW_KEYPAD_SLIDE,	-1, 1, "MagSw1",	EV_SW,  0, 20},