mmc: dw_mmc: fix the IDMAC sw reset

IDMAC may not be cleaned in driver probe if it has been already used in
boot time. So IDMAC needs sw reset newly. And DMA interface reset
precedes the internal DMAC reset. Additionally SDMMC_IDMAC_SWRESET is
replaced with magic code.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Acked-by: Will Newton <will.newton@gmail.com>
Signed-off-by: Chris Ball <cjb@laptop.org>