ARM: dts: imx6q-sabrelite: PHY reset is active-low

Note that the fec driver code currently hard-codes an active-low
reset, regardless of the flags in the device tree.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>