ALSA: hda - Enable mic mute hotkey and LEDs for an HP machine

ALSA: hda - Enable mic mute hotkey and LEDs for an HP machine

On this machine, the mic mute hotkey is connected to GPIO2. We therefore
create an extra input device for this key.

Also enable LEDs connected to GPIO3 and GPIO4.

(Note: if this patch is backported to older kernels, where KEY_MIC_MUTE is
not available, change the KEY_MIC_MUTE to KEY_F20, which was previously used
for mic mute keys.)

BugLink: https://bugs.launchpad.net/bugs/1408295
Tested-by: Keng-Yu Lin <keng-yu.lin@canonical.com>
Signed-off-by: David Henningsson <david.henningsson@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>