sh/PCI: Pass GAPSPCI_DMA_BASE CPU & bus address to dma_declare_coherent_memory()
dma_declare_coherent_memory() needs both the CPU physical address and the
bus address of the device memory. They are the same on this platform, but
in general we should use pcibios_resource_to_bus() to account for any
address translation done by the PCI host bridge.
This makes no difference on Dreamcast, but is safer if the usage is copied
to future drivers.