xtensa: Add config files for Diamond 233L - Rev C processor variant

The Diamond 233L processor is a pre-configured Xtensa processor tailored
for Linux application.

Signed-off-by: Pete Delaney <piet@tensilica.com>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>