IB/hfi1: Make the MSIx resource allocation a bit more flexible

The current method of allocating MSIx resources is a bit cumbersome,
and not very easily added to.

Refactor and re-order the code paths into a more consistent interface.

Update the interface so that allocations are not order dependent.

Reviewed-by: Mike Marciniszyn <mike.marciniszyn@intel.com>
Reviewed-by: Sadanand Warrier <sadanand.warrier@intel.com>
Signed-off-by: Michael J. Ruhl <michael.j.ruhl@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>