MFC 262785 263183 264182 264999 265391 265392 265395 265397 265398 265402 265403
    265442 265546 265680 265681 265719 265862 265864 265867 265927 266010 266495
    266540 266835 266856 266861 266862 267007 267310.

265391
  Define a new method for probing vt(4) driver before attach it at early stage.
265392
  Create dataset for vt(4) drivers.
265395
  Set of updates to vt(4) core part.
  o Declare vt(4) drivers dataset.
  o Create single static structures for all early drivers.
  o Add vt(4) to be by default in the kernel consoles list.
  o Create one more sysinit point, to be able to initialize memory and lock
  	requirement of early drivers.
  o Implement early drivers select. (Only best available will be selected).
  o Fix one missed "return (0)" for VTYLOCK.
  o Improve locking for cases when one driver replace another.
  o Make driver replacement notification less debug-look-like.
  o Minor spell fixes.
265397
  Switch fb and efifb drivers to use names and new vt(4) driver probe method.
265398
  Add vt(4) driver name for ofwfb driver.
265402
  Revert r264997 and r265026. It is not required anymore.
265403
  Switch vga drivers to use names and new vt(4) driver probe method.
265442
  Implement KDMKTONE ioctl.
265546
  Fix possible divide by zero.
265680
  No need to assign fields required and checked on probe.
265681
  Fix scrollback.
265719
  Hide debug messages under VT_DEBUG.
265927
  Update terminal sizes in any case when new vt(4) driver arrive.
  (Plus remove one unused newline)
266010
  Remove extra newlines.
  No functional changes.
266495
  Fix tty locking.
  o Correct expected values for VT_LOCKSWITCH ioctl.
  o Check current window for locked state.
266540
  Proper fix of VT_LOCKSWITCH ioctl.
266835
  Remove driver as unused.
267007
  Fix case when vt(4) started w/o driver assigned.
  o Always init locks and cv ASAP.
  o Initialize driver-independent parts even if driver probing fail.
  o Allow to call vt_upgrade anytime, for later loaded drivers.
  o New window flag VWF_READY, to track if window already initialized.
  Other updates:
  o Pass vd as a cookie for kbd_allocate.
  o Do not blank window on driver replacement.

Sponsored by:	The FreeBSD Foundation