PCI/MSI: Rename msi_set_enable(), msix_clear_and_set_ctrl()

Rename msi_set_enable() to pci_msi_set_enable() and
msix_clear_and_set_ctrl() to pci_msix_clear_and_set_ctrl().

No functional change.

[bhelgaas: changelog, split into separate patch]
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Fam Zheng <famz@redhat.com>