ARM: dts: imx6qdl-wandboard: use GPIO_6 for FEC interrupt

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.

Tested on a Wandboard Quad. Before the patch:

root@arm:~# ping -q -f -c 10000 192.168.2.1
PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.

=== 192.168.2.1 ping statistics ===
10000 packets transmitted, 10000 received, 0% packet loss, time 97363ms
rtt min/avg/max/mdev = 0.290/9.586/10.198/1.432 ms, pipe 2, ipg/ewma 9.737/9.672 ms

After the patch:

root@arm:~# ping -q -f -c 10000 192.168.2.1
PING 192.168.2.1 (192.168.2.1) 56(84) bytes of data.

=== 192.168.2.1 ping statistics ===
10000 packets transmitted, 10000 received, 0% packet loss, time 4810ms
rtt min/avg/max/mdev = 0.246/0.355/0.863/0.044 ms, ipg/ewma 0.481/0.319 ms

Signed-off-by: Sascha Silbe <x-linux@infra-silbe.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>