sdhci: Allow platform_set_power callback

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
sdhci-imx: Add power-gpio support

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
nitrogen6x: use power-gpio instead of vqmmc-supply to control WL_EN pin

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
nitrogen6_max: use power-gpio instead of vqmmc-supply to control WL_EN pin

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>