mmc: dw_mmc: add support for hi3798cv200 specific extensions of dw-mshc

Hi3798CV200 SoC extends the dw-mshc controller for additional clock
and bus control. Add support for these extensions.

Signed-off-by: tianshuliang <tianshuliang@hisilicon.com>
Signed-off-by: Jiancheng Xue <xuejiancheng@hisilicon.com>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Reviewed-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>