Introduce get_boot_device() to obtain the booting device. Make it also
available for non SPL builds so u-boot can also know the device it
is booting from.
Signed-off-by: Garrett Giordano <ggiordano@phytec.com>
Reviewed-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Andrew Davis <afd@ti.com>
