mmc: Revert "mmc: dw_mmc: Add check for IDMAC configuration"

This reverts commit 94c6cee9

 (Add check for IDMAC configuration).
Synopsys says that only if internal dmac is not present, optional
external dma interface is present. When internal dmac is present,
'0' value in DMA_INTERFACE of HCON is reasonable. DMA_INTERFACE
indicates external dma interface. And idmac initialization is
prohibited now.

The commit should be reverted since: the check for IDMAC is not
reliable; falling back to PIO would provide awful performance; we
wouldn't expect to see instances of this block without DMA support.

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