vt: add color support to the "underline" and "italic" attributes

Add color support to the "underline" and "italic" attributes as in
OpenBSD/NetBSD-style (vt220) and xterm.

Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Acked-by: "Antonino A. Daplas" <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>