mmc: sdhci-sprd: Add SD HS mode online tuning

First of all, Unisoc's IC provides cmd delay and read delay to ensure
that the host can get the correct data. However, according to SD Spec,
there is no need to do tuning in high speed mode, but with the
development of chip processes, it is more and more difficult to find
a suitable delay to cover all the chips. Therefore, we need SD high
speed mode online tuning.

In addition, we added mmc_sd_switch() and mmc_send_status() to the
header file to allow it to be usable by the driver.

Signed-off-by: Wenchao Chen <wenchao.chen@unisoc.com>
Link: https://lore.kernel.org/r/20230825091743.15613-3-wenchao.chen@unisoc.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>