ARM: 6438/2: mmci: add SDIO support for ST Variants

This adds some minor variant data and trickery to enable SDIO
on the ST Micro variants of MMCI/PL180.

Signed-off-by: Marcin Mielczarczyk <marcin.mielczarczyk@tieto.com>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>