octeon: apply vendor_model scheme to device definition/image name
This updates the device definition name for octeon target to provide
more useful names for the images and be consistent with the increasing
number of targets following that scheme.
Since the target is not using device tree yet, this does not touch
board_name and thus sets BOARD_NAME in image Makefile to ensure
sysupgrade is still working.
While at it, move Build block before Device blocks and remove trailing
whitespace for CMDLINE.
Signed-off-by: Adrian Schmutzler <firstname.lastname@example.org>