compat_sys_ioctl(): make parallel to do_vfs_ioctl()

Handle ioctls that might be handled without reaching ->ioctl() in
native case on the top level there.  The counterpart of vfs_ioctl()
(i.e. calling ->unlock_ioctl(), etc.) left as-is; eventually
that would turn simply into the call of ->compat_ioctl(), but
that'll take more work.  Once that is done, we can move the
remains of compat_sys_ioctl() into fs/ioctl.c and finally bury
fs/compat_ioctl.c.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>