sh: Move IRQ multi definition of DMAC to defconfig

When SuperH CPU has IRQ multi of DMAC, SH_DMA_IRQ_MULTI becomes enable.
The following CPU's are Multi IRQ of DMAC now.
 - SH775X and SH7091
 - SH776X
 - SH7780
 - SH7785

If SH_DMA_IRQ_MULTI becomes enable, dma-sh api driver is optimized
for Multi IRQ.

Signed-off-by: Nobuhiro Iwamatsu <iwamatsu.nobuhiro@renesas.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>