tty: vt: keyboard: Allow Unicode compose base char

Pass Unicode character to k_unicode handler function to honor possible
accent_table definition.

With introduction of KDSKBDIACRUC ioctl, it has been possible to set
compose characters (diacr, base and result) to any Unicode character
(below 0xf000 code point) as defined in struct kbdiacruc.

But it does not work with characters beyond Latin-1 as base, because
they are printed early and not passed to any of the handler functions,
thus breaking compose and dead keys.

It affects keyboard layouts defining such characters on level 1 and
relying on dead keys to access level 3 (e.g., lv-modern with some
modifications for extra characters on level 3 for ē, ā and ī keys).

Signed-off-by: Reinis Danne <rei4dan@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>