PCI: Add PTM clock granularity information

The PTM Control register (PCIe r3.1, sec 7.32.3) contains an Effective
Granularity field:

  This provides information relating to the expected accuracy of the PTM
  clock, but does not otherwise affect the PTM mechanism.

Set the Effective Granularity based on the PTM Root and any intervening PTM
Time Sources.

This does not set Effective Granularity for Root Complex Integrated
Endpoints because I don't know how to figure out clock granularity for
them.  The spec says:

  ... system software must set [Effective Granularity] to the value
  reported in the Local Clock Granularity field by the associated PTM
  Time Source.

but I don't know how to identify the associated PTM Time Source.  Normally
it's the upstream bridge, but an integrated endpoint has no upstream
bridge.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>

include/linux/pci.h

@@ -371,6 +371,7 @@ struct pci_dev {
 #ifdef CONFIG_PCIE_PTM
 	unsigned int	ptm_root:1;
 	unsigned int	ptm_enabled:1;
+	u8		ptm_granularity;
 #endif
 #ifdef CONFIG_PCI_MSI
 	const struct attribute_group **msi_irq_groups;