move compat handling of tty ioctls to tty_compat_ioctl()

ioctls that are
	* callable only via tty_ioctl()
	* not driver-specific
	* not demand data structure conversions
	* either always need passing arg as is or always demand compat_ptr()
get intercepted in tty_compat_ioctl() from the very beginning and
redirecter to tty_ioctl().  As the result, their entries in fs/compat_ioctl.c
(some of those had been missing, BTW) got removed, as well as
n_tty_compat_ioctl_helper() (now it's never called with any cmd it would accept).

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>