tty: vt, separate T.416 high colors handler

The code with T.416 high colors handling is flushed to the right and
hard to read. Move the code to a separate function and remove code
duplication for foreground & background colors.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>