sh: Tidy up some of the cpu legacy dma header mess.

This has turned in to quite a mess, and with CPUs that care using
dmaengine now it's about time to start cleaning up after the legacy DMA
code. For starters, kill off the stubs for the CPUs that don't do
anything, as well as all of the unused definitions. This leaves us with a
set of IRQs and base addresses we can deal with later.

Signed-off-by: Paul Mundt <lethal@linux-sh.org>