PCI: dra7xx: PCI_EXP_LNKCTL2 usage

[Bjorn Helgaas]

ab5fe4f4d31e ("PCI: dra7xx: Add support to force RC to work in GEN1 mode")
added this:

  +       dw_pcie_cfg_read(pp->dbi_base + exp_cap_off + PCI_EXP_LNKCTL2,
  +                        2, &reg);
  +       if ((reg & PCI_EXP_LNKCAP_SLS) != PCI_EXP_LNKCAP_SLS_2_5GB) {
  +               reg &= ~((u32)PCI_EXP_LNKCAP_SLS);
  +               reg |= PCI_EXP_LNKCAP_SLS_2_5GB;
  +               dw_pcie_cfg_write(pp->dbi_base + exp_cap_off +
  +                                 PCI_EXP_LNKCTL2, 2, reg);
  +       }

This probably works as intended, but it *looks* wrong because it uses
LNKCAP_* symbols on LNKCTL2 register values.  We do have
PCI_EXP_LNKCTL2_* symbols, so I think it would be better if we used
used those.

Bjorn