mmc: rockchip: add SDHCI driver support for rockchip soc

mmc: rockchip: add SDHCI driver support for rockchip soc

Rockchip rk3399 using arasan sdhci-5.1 controller.
This patch add the controller support to enable mmc device
with full driver-model support, tested on rk3399 evb board.

According to my test result, this driver should be OK,
the command "part list mmc 0" can result in a right output,
but all the mmc command failed like this:
	=> mmc info
	No MMC device available
	Command failed, result=1

The result of get_mmc_num in cmd/mmc.c is always 0?

Signed-off-by: Kever Yang <kever.yang@rock-chips.com>
Acked-by: Simon Glass <sjg@chromium.org>