u8500: Separating mmc config parameters from driver

Configuration in vexpress and u8500.v1 is different from what
is needed in u8500.v2.  As such, card configuration specifics need
to reside in the board file rather than the driver.

Signed-off-by: John Rigby <john.rigby@linaro.org>
Signed-off-by: Mathieu Poirier <mathieu.poirier@linaro.org>
Signed-off-by: Tom Rini <trini@ti.com>