Android: implement headphone detection thus enabling pause on unplug (FS#12097).

Listen to headphone plug events. There are currently two glitches with this:
- Android takes a while until it reports the unplug event, so there will be
  some delay until playback gets paused. This is an Android limitation.
- Rockbox debounces headphone state changes for one second. Therefore playback
  will shortly be routed to the speaker on unplug until Rockbox does the actual
  pause.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@29956 a1c6a512-1295-4272-9138-f99709370657
3 files changed