arm: mvebu: add pin muxing options for the SDIO interface on Armada 370

The SDIO interface is available either on pins MPP9/11/12/13/14/15 or
MPP47/48/49/50/51/52 on the Armada 370. Even though all combinations
are potentially possible, those two muxing options are the most
probable ones, so we provide those at the SoC level .dtsi file.

In practice, in turns out the Armada 370 DB board uses the former,
while the Armada 370 Mirabox uses the latter.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>