Support MSI-X for passthrough devices with a separate PBA BAR.

Support MSI-X for passthrough devices with a separate PBA BAR.

pci_alloc_msix() requires both the table and PBA BARs to be allocated
by the driver.  ppt was only allocating the table BAR so would fail
for devices with the PBA in a separate BAR.  Fix this by allocating
the PBA BAR before pci_alloc_msix() if it is stored in a separate BAR.

While here, release BARs after calling pci_release_msi() instead of
before.  Also, don't call bus_teardown_intr() in error handling code
if bus_setup_intr() has just failed.

Reported by:	gallatin
Tested by:	gallatin
Reviewed by:	rgrimes, markj
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D20525