Add a simple unaccelerated vt(4) framebuffer driver for Sun framebuffers
handled by creator(4) (Sun Creator 3D, Elite 3D, etc.). This provides
vt(4) consoles on all devices currently supported by syscons on sparc64.
The driver should also be easily adaptable to support newer Sun framebuffers
such as the XVR-500 and higher.

Many thanks to dumbbell@ (Jean-Sebastien Pedron) for testing this remotely
during development.