compat_ioctl: move cdrom commands into cdrom.c

There is no need for the special cases for the cdrom ioctls any more now,
so make sure that each cdrom driver has a .compat_ioctl() callback and
calls cdrom_compat_ioctl() directly there.

Reviewed-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>