Fix audio routing issues

Firstly, make input source VOICE_COMMUNICATION work correctly. Notably,
this fixes Android's integrated SIP client.

Secondly, really disable combo device support in libaudio. This
disables the internal speaker for notifications and the like if
headphones are attached.

Change-Id: I6391c5d442594ef2b1852d66f7480964833427bd
Merge commit 'refs/changes/42/5142/2' of http://cas-online.nl:8181/androidarmv6/android_device_samsung_msm7x27-common into cm-10.1