pcie: Rename the pcie_cap_ari_* functions to pcie_cap_arifwd_*

Rename helper functions to make a clearer distinction between
the PCIe capability/control register feature ARI forwarding and a
device that supports the ARI feature via an ARI extended PCIe capability.

Signed-off-by: Knut Omang <knut.omang@oracle.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>