mmc: sdhci: Rename sdhci_set_power() to sdhci_set_power_noreg()

Unlike other cases, sdhci_set_power() does not reflect the default
implementation of the ->set_power() callback. Rename it and create
sdhci_set_power() that is the default implementation.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jisheng Zhang <jszhang@marvell.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>