Currently MMC_MXC driver can be selected by all i.MX devices.

Restrict its use only for the appropriate processors.
Signed-off-by: NFabio Estevam <fabio.estevam@freescale.com>
Acked-by: NSascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: NChris Ball <cjb@laptop.org>