PCI/MSI: Rename pci_msi_check_device() to pci_msi_supported()

Rename pci_msi_check_device() to pci_msi_supported() for clarity.  Note
that pci_msi_supported() returns true if MSI/MSI-X is supported, so code
like:

  if (pci_msi_supported(...))

reads naturally.

[bhelgaas: changelog, split to separate patch, reverse sense]
Signed-off-by: Alexander Gordeev <agordeev@redhat.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>