atmel-mci: add MCI2 register definitions

New revision of Atmel MCI interface adds new features. This is a update of
register definition in header file. This new MCI IP is called MCI2.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Pierre Ossman <pierre@ossman.eu>