Some early 2.x sun4c PROM will default to serial input but glass output if no keyboard is connected but a framebuffer exists in the machine; the current kernel console code will complain and switch to full serial, but later on the framebuffer would incorrectly take over the console.
Some early 2.x sun4c PROM will default to serial input but glass output if no
keyboard is connected but a framebuffer exists in the machine; the current
kernel console code will complain and switch to full serial, but later on
the framebuffer would incorrectly take over the console.

Correctly detect this situation and reset the `fbnode' variable. This is
an improvement of the fix which went in rev 1.54 of this file.

orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars,orumin/openbsd-efivars