mvebu: pinctrl: Add SD/eMMC PHY selector to the driver

When the pin control driver selects SD/eMMC function for
a pin group, there is additional configuration to be done
for this case - switch the PHY to work with SDHCI interface.
This patch adds the missing functionality into the pin
control driver.

Signed-off-by: Konstantin Porotchkin <kostap@marvell.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Signed-off-by: Evan Wang <xswang@marvell.com>
Signed-off-by: Stefan Roese <sr@denx.de>