V4L/DVB: v4l2_subdev: Move interrupt_service_routine ptr to v4l2_subdev_core_ops

The CX2584x and related cores are multifunction subdevices with a number
of internal blocks that act as interrupt sources.  Move the v4L2_subdev
interrupt_service_routine callback from v4l_subdev_ir_ops to
v4l2_subdev_core_ops, as the video and audio blocks of a CX2584x and
related cores can generate interrupts along with the IR block.  This
change also makes sense for other subdev's that generate interrupts and
do not have an IR block.

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