powerpc/5200: add LocalPlus bus FIFO device driver

This is a driver for the FIFO device on the LocalPlus bus on an mpc5200 system.
The driver supports programmed I/O through the FIFO as well as setting up DMA
via the BestComm engine through the FIFO.

Signed-off-by: John Bonesio <bones@secretlab.ca>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>