mmc: dw_mmc: k3: UHS-SD card for Hisilicon Hikey

Hisilicon Hikey have no tuning function in dw_mmc-k3.c,
so we must do the tuning function stub when we init UHS card.

Signed-off-by: Jin Guojun <kid.jin@hisilicon.com>
Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>