PCI: Add Vendor-Specific Extended Capability header info

This adds the fields in the Vendor-Specific Header: ID, Rev, and Length.
There may be multiple Vendor-Specific capabilities, so drivers should use
the VSEC ID to identify the one of interest.
Signed-off-by: NBjorn Helgaas <bhelgaas@google.com>

include/linux/pci_regs.h

@@ -677,6 +677,12 @@
 #define  PCI_PWR_CAP_BUDGET(x)	((x) & 1)	/* Included in system budget */
 #define PCI_EXT_CAP_PWR_SIZEOF	16
 
+/* Vendor-Specific (VSEC, PCI_EXT_CAP_ID_VNDR) */
+#define PCI_VNDR_HEADER		4	/* Vendor-Specific Header */
+#define  PCI_VNDR_HEADER_ID(x)	((x) & 0xffff)
+#define  PCI_VNDR_HEADER_REV(x)	(((x) >> 16) & 0xf)
+#define  PCI_VNDR_HEADER_LEN(x)	(((x) >> 20) & 0xfff)
+
 /*
  * Hypertransport sub capability types
  *