MAINTAINERS: TTY LAYER: add some ./include/linux/ header files

MAINTAINERS: TTY LAYER: add some ./include/linux/ header files

An early prototypical automated code analysis of headers and the
existing MAINTAINERS sections identified some header files in
./include/linux/ to be probably included into the TTY LAYER section.

I further checked those suggestions by this analysis and identified a
subset of files that I am rather certain to belong to the TTY LAYER.

Add these ./include/linux/ header files to TTY LAYER in MAINTAINERS.

The patterns include/linux/tty*.h and include/linux/vt_*.h currently cover:

  include/linux/tty.h
  include/linux/tty_driver.h
  include/linux/tty_flip.h
  include/linux/tty_ldisc.h

  include/linux/vt_buffer.h
  include/linux/vt_kern.h

Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Link: https://lore.kernel.org/r/20210518052117.14819-2-lukas.bulwahn@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>