ARM: add DMA support to sh7372, enable DMA for SDHI

This adds DMA support for the sh7372 sh-mobile ARM core, using the shdma
dmaengine driver, and uses DMA for the SDHI SD-card controller on this SoC.

Signed-off-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>