MIPS: Octeon: Use model string from DTB for unknown board type

Use model string from DTB for board type if the board is unknown.
This is more informative, e.g. with EdgeRouter Pro the /proc/cpuinfo
will display "ubnt,e200 (CN6120p1.1-1000-NSP)" instead of misleading
"Unsupported Board".

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: David Daney <ddaney.cavm@gmail.com>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/12582/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>