ARM: dts: imx6: delete interrupts property if interrupts-extended is set

In most cases this is related to fsl,err006687-workaround-present, which
requires a GPIO interrupt next a GIC interrupt.

This fixes the dtbs_check warning:
imx6dl-mba6a.dtb: ethernet@2188000: More than one condition true in oneOf schema:
        {'$filename': 'Documentation/devicetree/bindings/net/fsl,fec.yaml',
[...]

Signed-off-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>