ARM: dts: dra7: Add properties to enable PCIe x2 lane mode

ti,syscon-lane-sel and ti,syscon-lane-conf properties specific to enable
PCIe x2 lane mode are added here.

Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>