mmc: sdhci-cadence: Enable device specific override of writel()

mmc: sdhci-cadence: Enable device specific override of writel()

SoCs with device specific Cadence implementation, such as setting
byte-enables before the write, need to override writel().  Add a
callback where the default is writel() for all existing chips.

Signed-off-by: Brad Larson <blarson@amd.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20230410184526.15990-12-blarson@amd.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>