vt: fix canonical input in UTF-8 mode

For e.g.  proper TTY canonical support, IUTF8 termios flag has to be set as
appropriate.  Linux used to not care about setting that flag for VT TTYs.

This patch fixes that by activating it according to the current mode of the
VT, and sets the default value according to the vt.default_utf8 parameter.

Signed-off-by: Samuel Thibault <samuel.thibault@ens-lyon.org>
Cc: Willy Tarreau <w@1wt.eu>
Cc: <stable@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>