at91/atmel-mci: inclusion of sd/mmc driver in at91sam9g45 chip and board

This adds the support of atmel-mci sd/mmc driver in at91sam9g45 devices and
board files. This also configures the DMA controller slave interface for
at_hdmac dmaengine driver.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>