bus/pci: always check IOMMU capabilities

bus/pci: always check IOMMU capabilities

IOMMU capabilities won't change and must be checked even if no PCI device
seem to be supported yet when EAL initialised.

This is to accommodate with SPDK that registers its drivers after
rte_eal_init(), especially on PPC platform where the IOMMU does not
support VA.

Fixes: 703458e19c16 ("bus/pci: consider only usable devices for IOVA mode")

Signed-off-by: David Marchand <david.marchand@redhat.com>
Reviewed-by: David Christensen <drc@linux.vnet.ibm.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>
Tested-by: Jerin Jacob <jerinj@marvell.com>
Tested-by: Takeshi Yoshimura <tyos@jp.ibm.com>