The current implementation of the bootloader specification depends on the
hardware name and the name of the device in /dev to match. As the default
hardware name is mciX and the device name is diskY the bootloader spec
cannot be used as is.

This patch implements a way to overwrite the device name similar to what is
possible for the imx-esdhc driver.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>