mmc: dw_mmc: change to use recommended reset procedure

This patch changes the fifo reset code to follow the reset procedure
outlined in the documentation of Synopsys Mobile storage host databook.

Signed-off-by: Sonny Rao <sonnyrao@chromium.org>
Signed-off-by: Yuvaraj Kumar C D <yuvaraj.cd@samsung.com>
Acked-by: Seungwon Jeon <tgih.jun@samsung.com>
[sonnyrao: fix compile for !CONFIG_MMC_DW_IDMAC case]
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>