uboot-imx

imx: s/docs\/README.imximage/doc\/README.imximage/g

Fixed typo for doc/README.imximage on respective imximage.cfg files.

Cc: Tom Rini <trini@konsulko.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Acked-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>