powerpc/PCI: Disable MSI/MSI-X interrupts at PCI probe time in OF case

Since commit 1851617c ("PCI/MSI: Disable MSI at enumeration even if
kernel doesn't support MSI"), the setup of dev->msi_cap/msix_cap and the
disable of MSI/MSI-X interrupts isn't being done at PCI probe time, as
the logic responsible for this was moved in the aforementioned commit
from pci_device_add() to pci_setup_device(). The latter function is not
reachable on PowerPC pseries platform during Open Firmware PCI probing
time.

This exhibits as drivers not being able to enable MSI, eg:

  bnx2x 0000:01:00.0: no msix capability found

This patch calls pci_msi_setup_pci_dev() explicitly to disable MSI/MSI-X
during PCI probe time on pSeries platform.

Fixes: 1851617c ("PCI/MSI: Disable MSI at enumeration even if kernel doesn't support MSI")
[mpe: Flesh out change log and clarify comment]
Signed-off-by: Guilherme G. Piccoli <gpiccoli@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>