m4: update audio policy

Pretty much lifted verbatim from m7.

Change-Id: I0b5cd14ed62ac558ac5f5cd7b7561b4aacd2a6f7
m4: init cleanup

* remove duplication and a bunch of stuff that flat out doesn't exist
* tighten permissions where possible

Change-Id: Icc03cbcec6385ad0df3b84ec0bd03e726f44fd0e
m4: update overlay

* remove overrides that duplicate the default values or don't exist
* we have variable button brightness, mention it
* (add missing|fix bluetooth) network attributes

Change-Id: Iedf51060db1480e07f275369d0a0e109f56d9f20
Merge changes Iedf51060,Icc03cbce,I0b5cd14e into cm-11.0

* changes:
  m4: update overlay
  m4: init cleanup
  m4: update audio policy