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/1408295Tested-by: NKeng-Yu Lin <keng-yu.lin@canonical.com>
Signed-off-by: NDavid Henningsson <david.henningsson@canonical.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>