MFC r314116:

MFC r314116:
  Fix a panic during boot caused by inadequate locking of some vt(4) driver
  data structures.

  vt_change_font() calls vtbuf_grow() to change some vt driver data
  structures. It uses TF_MUTE to prevent the console from trying to use
  those data structures while it changes them.

  During the early stage of the boot process, the vt driver's tc_done
  routine uses those data structures; however, it is currently called
  outside the TF_MUTE check.

  Move the tc_done routine inside the locked TF_MUTE check.

PR:		217282
Sponsored by:	Netflix, Inc.