The Android 3.5mm Headset jack specification mentions that BTN_0 should
be mapped to KEY_MEDIA, but this is less logical than KEY_PLAYPAUSE,
which has much broader userspace support.
For example, the Chrome OS userspace now supports KEY_PLAYPAUSE to toggle
play/pause of videos and audio, but does not handle KEY_MEDIA.
Furthermore, Android itself now supports KEY_PLAYPAUSE equivalently, as the
new USB headset spec requires KEY_PLAYPAUSE for BTN_0.
https://source.android.com/devices/accessories/headset/usb-headset-spec
[PATCH 1/5] ASoC: Intel: kbl_rt5663_rt5514_max98927: Map BTN_0 to
[PATCH 2/5] ASoC: Intel: kbl_rt5663_max98927: Map BTN_0 to
[PATCH 3/5] ASoC: ts3a227e: Map BTN_0 to KEY_PLAYPAUSE
[PATCH 4/5] ASoC: rk3399_gru_sound: Map BTN_0 to KEY_PLAYPAUSE
[PATCH 5/5] ASoC: qcom: apq8016-sbc: Map BTN_0 to KEY_PLAYPAUSE
