tty: tty_ldisc: Fix some kernel-doc related misdemeanours

tty: tty_ldisc: Fix some kernel-doc related misdemeanours

 - Functions must follow directly on from their headers
 - Demote non-conforming kernel-doc header
 - Ensure notes have unique section names
 - Provide missing description for 'reinit'

Fixes the following W=1 kernel build warning(s):

 drivers/tty/tty_ldisc.c:158: warning: cannot understand function prototype: 'int tty_ldisc_autoload = IS_BUILTIN(CONFIG_LDISC_AUTOLOAD); '
 drivers/tty/tty_ldisc.c:199: warning: Function parameter or member 'ld' not described in 'tty_ldisc_put'
 drivers/tty/tty_ldisc.c:260: warning: duplicate section name 'Note'
 drivers/tty/tty_ldisc.c:717: warning: Function parameter or member 'reinit' not described in 'tty_ldisc_hangup'

Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20201112105857.2078977-2-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>