dmaengine: shdma: Introduce include/linux/sh_dma.h

Create a common platform data header file for the
shdma dmaengine driver. This is done by moving
common structures from sh asm/dmaengine.h to
linux/sh_dma.h. DMA registers are also copied from
sh asm/dma-register.h to make the code architecture
independent.

The sh header file asm/dmaengine.h is still kept
with the slave id enum. This allows us to keep the
old processor specific code as is and slowly move
over to slave id enums in per-processor headers.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>