ARM: at91: add atmel-mci support for chips and boards which can use it

Since atmel-mci driver supports all atmel mci versions,
use it instead of the deprecated at91_mci driver.
Platform data and all related configuration are removed.

Signed-off-by: Ludovic Desroches <ludovic.desroches@atmel.com>
[nicolas.ferre@atmel.com: remove at91_mci platform data]
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>