PCI: dwc: Add a 'num_lanes' field to struct dw_pcie

Add a 'num_lanes' field to allow drivers to provide a the number of lanes
if not in DT or using a custom DT property. A driver can provide a
non-zero value which is used if the DT doesn't have a 'num-lanes'
property.

Link: https://lore.kernel.org/r/20200821035420.380495-24-robh@kernel.org


Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>