Map the buttons from the Android reference headset to
KEY_PLAYPAUSE, KEY_VOICECOMMAND, KEY_VOLUMEUP, and KEY_VOLUMEDOWN.
KEY_PLAYPAUSE is used instead of KEY_MEDIA for BTN_0 as it is more
logical and have much broader userspace support. Like Chrome OS
use it to play/pause of video and audio. KEY_PLAYPAUSE is also
supported by Android (USB headset spec requires KEY_PLAYPAUSE
for BTN_0.)
https://source.android.com/devices/accessories/headset/usb-headset-spec
Signed-off-by: Chinyue Chen <chinyue@xxxxxxxxxxxx>
Signed-off-by: Benson Leung <bleung@xxxxxxxxxxxx>
Signed-off-by: Radoslaw Biernacki <rad@xxxxxxxxxxxx>