Initialise these variables so gcc doesn't complain.

Submitted by:	luigi
Add vt(4) devices and options to NOTES

Reviewed by:	marius (earlier version)
Prefer vt(4) for UEFI boot

The UEFI framebuffer driver vt_efifb requires vt(4).  This change is
rather ugly; console init happens very early in the boot which makes a
cleaner interface difficult.  This change is intended only to facilitate
the sc(4) / vt(4) transition, and can be reverted once vt(4) is the
default.
Prefer vt(4) to sc(4) by default

And revert the UEFI sc/vt transition kludge rXXXXXX.