mx51_babbage: Add SPI flash support

MX51 Babbage has an AT45DB321 SPI Flash connected to eCSPI1.

Add support for it.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>