[SCSI] qla2xxx: Use standard PCIe Capability Link register field names

Use the standard #defines for PCIe Link Capability register fields
rather than bare numbers.  This also uses the new PCI Express Capability
accessor rather than reading the capability directly.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Saurav Kashyap <saurav.kashyap@qlogic.com>
Acked-by: Giridhar Malavali <giridhar.malavali@qlogic.com>