ARM: dts: imx6sx-udoo-neo: Pass the 'phy-reset-duration' property

imx6sx-udoo-neo has a KSZ8091 Ethernet PHY, which requires the reset
signal to be low for at least 10ms.

Pass the 'phy-reset-duration' property to reflect such requirement.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>