pasemi_mac: Convert to new dma library

Convert the pasemi_mac driver to the new platform global DMA manaagement
library. This also does a couple of other minor cleanups w.r.t. channel
management.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>