imx: Use a clear identification of an unidentified CPU type

In case an unidentified CPU type is detected it now returns
i.MX??, in a const char.

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
1 file changed