Refactor the IRQ initialization code:

* Move the looking up of the vIRQs to the beginning of probe(), failing
  probe early if this fails
* Do the actual requesting of IRQs inline in probe() and properly abort
  probe() on errors
* Use devm_request_threaded_irq(), completing the conversion of probe() to
  only use devm managed resources and remove the remove() driver function.
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>