libata: do not suspend port if normal ODD is attached

For ODDs, the upper layer will poll for media change every few
seconds, which will make it enter and leave suspend state very
often. And as each suspend will also cause a hard/soft reset,
the gain of runtime suspend is very little while the ODD may
malfunction after constantly being reset. So the idle callback
here will not proceed to suspend if a non-ZPODD capable ODD is
attached to the port.

Signed-off-by: Aaron Lu <aaron.lu@intel.com>
Acked-by: Tejun Heo <tj@kernel.org>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>