Make pasemi_mac.c depend on PPC_PASEMI to prevent link errors

drivers/net/pasemi_mac.c is enabled by CONFIG_PASEMI_MAC, which depends on
PPC64 && PCI. However pasemi_mac.c uses several routines that are only
built when PPC_PASEMI is selected. This can lead to an unbuildable config:

 ERROR: ".pasemi_dma_start_chan" [drivers/net/pasemi_mac.ko] undefined!

So make CONFIG_PASEMI_MAC depend on PPC_PASEMI instead of PPC64.

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Jeff Garzik <jeff@garzik.org>