You can take the following steps at OpenBoot PROM to designate a framebuffer as a console:
OK show-displays
Select the graphics accelerator, e.g. b
OK nvalias mydev <CTRL-Y>
OK setenv output-device mydev
OK setenv use-nvramrc? true
OK reset-all
OK show-displays
Select the graphics accelerator, e.g. b
OK nvalias mydev <CTRL-Y>
OK setenv output-device mydev
OK setenv use-nvramrc? true
OK reset-all