mmc: sdhci: iproc: Add custom set_power() callback for bcm2711

mmc: sdhci: iproc: Add custom set_power() callback for bcm2711

The controller needs a valid bus voltage in its power register
regardless of whether an external regulator is taking care of the power
supply.

The sdhci core already provides a helper function for this,
sdhci_set_power_and_bus_voltage(), so create a bcm2711 specific 'struct
sdhci_ops' which makes use of it.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
Link: https://lore.kernel.org/r/20200306174413.20634-10-nsaenzjulienne@suse.de
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>