MFC r260607, r260610, r260934:

r260607:
The onyx codec works also as module, so add it.

r260610:
Described in the man page but not implemented. Here it comes,
atomic_swap_32/64. The latter only for powerpc64.

r260934:
Fix the resource information for the i2s-a node on certain G5 PowerMacs.
This is the first step needed to get the snapper codec working on those
machines.
The second step is to enable the corresponding I2S device and its clock.

Tested on machines where the snapper codec was already working, a G4 PowerBook
and a PowerMac9,1 with a Shasta based macio.
The PowerMac7,2/7,3 with a K2 based macio can now also play sound.