mmc: dw_mmc: add dw_mmc-k3 for k3 platform

Add dw_mmc-k3.c for k3v2, support sd/emmc

Signed-off-by: Zhangfei Gao <zhangfei.gao@linaro.org>
Signed-off-by: Zhigang Wang <brooke.wangzhigang@huawei.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chris Ball <chris@printf.net>