mmc: mmci: Enable Device Tree support for ux500 variants

Provide a means to collect attributes specific to ST-Ericsson's ux500
variant series. This patch registers itself as the AMBA driver to be
called during the probe process. Once all attributes and ux500 specifics
are are collected the normal mmci core probe is called.

Signed-off-by: Lee Jones <lee.jones@linaro.org>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Chris Ball <cjb@laptop.org>