dmaengine: shdma: Add more register documentation

Also add a few definitions that were missing.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

diff --cc arch/sh/include/asm/dma-register.h
Simple merge

diff --cc drivers/dma/sh/shdmac.c
Simple merge

diff --cc include/linux/sh_dma.h
Simple merge