Initial audio support on FP2

Should work pretty much OOTB now.

To enable speakers:

alsaucm -n -b - <<EOM
open FP2
set _verb HiFi
set _enadev Speaker
EOM

E.g. to switch from Speakers to Headphones:

alsaucm -n -b - <<EOM
open FP2
set _verb HiFi
set _enadev Speaker
set _disdev Speaker
set _enadev Headphones
EOM

(the enable-disable procedure is neccessary because alsaucm doesn't have any state and just disabling a device when it's supposedly not enabled doesn't do anything)

Earpiece is not yet supported in the config but should be pretty easy.