ARM: kirkwood: make use of DT mvsdio on guruplug board

Device tree based guruplug boards still use mvsdio platform_data and
kirkwood_sdio_init to enable sdio. DT support for sdio is already there,
so make use of it.

This also fixes mvsdio accidentially breaking nand by configuring mpp0
to gpio, while used also by nand (nand_io2 on mpp0).

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Tested-by: Soeren Moch <smoch@web.de>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>