ARM: dts: imx6: add fec gpr property.

This is required for wake on lan on i.MX6

Signed-off-by: Martin Fuzzey <martin.fuzzey@flowbird.group>
Reviewed-by: Fugang Duan <fugang.duan@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>