bt-vendor: Add support for BT RF power class.

Default value as 1. Possible values include 0, 1 & 2.
Set via [persist.service.bt.power].
common: update headers
overlay: battery: change low/critical values
use default webview and default MP3, AAC decoders

Seems that I cannot notice any problems with webviewchromium, hence enable it.
Use default MP3 and AAC decoders as the non-OMX one's are not working anymore

Also disable AV enhancements, useless for msm7x27a