This patch makes the dreamcast use the recently added declared coherent
memory functions to point out the memory window suitable for dma.

Apart from cleaning up, this gives the dreamcast a proper memory allocator
for pci dma memory.
Signed-off-by: NMagnus Damm <damm@igel.co.jp>
Signed-off-by: NPaul Mundt <lethal@linux-sh.org>