dt-bindings: PCI: mvebu: Add num-lanes property

Controller driver needs to correctly configure PCIe link if it contains 1
or 4 SerDes PCIe lanes. Therefore add a new 'num-lanes' DT property for
mvebu PCIe controller. Property 'num-lanes' seems to be de-facto standard
way how number of lanes is specified in other PCIe controllers.

Link: https://lore.kernel.org/r/20220222155030.988-5-pali@kernel.org


Signed-off-by: Pali Rohár <pali@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Rob Herring <robh@kernel.org>