PCI: dwc/intel-gw: Move getting PCI_CAP_ID_EXP offset to intel_pcie_link_setup()

PCI: dwc/intel-gw: Move getting PCI_CAP_ID_EXP offset to intel_pcie_link_setup()

The PCI_CAP_ID_EXP offset is only needed by intel_pcie_link_setup(), so
let's retrieve it there and avoid storing the offset.

Link: https://lore.kernel.org/r/20200821035420.380495-38-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Dilip Kota <eswara.kota@linux.intel.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>