Blackfin: stick the CPU name into boot image name

Rather than use "Linux" in the boot image name (as this is redundant --
the image type is already set to "linux"), use the CPU name.  This makes
it fairly obvious when a wrong image is accidentally booted.  Otherwise
there is no kernel output and you waste time scratching your head
wondering wtf just happened.

Signed-off-by: Robin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>