mmc: sdhci: Add helpers for the auto-CMD23 flag

Add 2 helper functions to make the use of the auto-CMD23 flag more
readable.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Tested-by: Baolin Wang <baolin.wang7@gmail.com>
Link: https://lore.kernel.org/r/20200412090349.1607-2-adrian.hunter@intel.com


Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>