V4L/DVB (9776): cx18: Change to per CX23418 device work queues for deferrable work handling

cx18: Change to per CX23418 device work queues for deferrable work handling.
Needed to support 2.6.22 and earlier kernels that can't selectively cancel
work orders.  Also will provide slightly better performance on SMP systems.

Signed-off-by: Andy Walls <awalls@radix.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>