memory: atmel-ebi: Add PM ops

Add a ->resume() hook to make sure the EBI dev configs are correctly
restored when resuming the platform.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>