ARM: dts: imx6qdl-wandboard: use GPIO_6 for FEC interrupt
Apply the same work-around for i.MX 6D/Q erratum 006687 as used for
Sabre Lite for the Wandboard Dual / Quad.
Like on the Sabre Lite, GPIO6 is used as a power down output for
camera expansion boards. However, these expansion boards do not work
with mainline yet anyway.