sh64: Move DMA macros from pci.h to scatterlist.h.

In order to be more consistent with other architectures, move two
DMA-related scatterlist macros from pci.h to scatterlist.h.

Signed-off-by: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>