pasemi_mac: Move register definitions to include/asm-powerpc

Move the common register formats and descriptor layouts from
drivers/net/pasemi_mac.h to include/asm-poewrpc/pasemi_dma.h

Previously only the ethernet driver was using them, but other drivers
are coming up that will also use them, so it makes sense to share the
constants.
Signed-off-by: Olof Johansson <olof@lixom.net>
Signed-off-by: Jeff Garzik <jeff@garzik.org>