TTY: provide tty_standard_install helper

There are currently many cut&paste copies of what
tty_driver_install_tty does when custom ->install method is not
provided. Let's get rid of the copies and create a helper with this
setup code.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Cc: Havard Skinnemoen <hskinnemoen@google.com>
Acked-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>