pci_enable_ari() now supports enabling or disabling ARI forwarding.  So
rename pci_enable_ari() to pci_configure_ari() for easy understanding.

No functional change.

[bhelgaas: changelog]
Signed-off-by: Yijing Wang <wangyijing@huawei.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>