The old __address element in struct scatterlist remained from older
kernels because the ARM DMA emulation code made use of it.  Move
this field into struct dma_struct, and convert DMA emulation code
to setup a SG entry as required.

Also, convert DMA emulation code to use the new DMA API rather
than the PCI DMA API.
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>