mmc: mvsdio: add pinctrl integration

On many Marvell SoCs, the pins used for the SDIO interface are part of
the MPP pins, that are muxable pins. In order to get the muxing of
those pins correct, this commit integrates the mvsdio driver with the
pinctrl infrastructure by calling devm_pinctrl_get_select_default()
during ->probe().

Note that we permit this function to fail because not all Marvell
platforms have yet been fully converted to using the pinctrl
infrastructure.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Andrew Lunn <andrew@lunn.ch>
Tested-by: Stefan Peter <s.peter@mpl.ch>
Tested-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>
Signed-off-by: Chris Ball <cjb@laptop.org>