ARM: dts: imx7-colibri: allow to disable Ethernet rail

The regulator-always-on property on the Ethernet rail prevents Linux
from disabling the rail when Ethernet is shut down (suspend or simply
link down). With this change the regulator framework will disable the
rail when the Ethernet PHY is not used, saving power especially on
carrier board not using Ethernet.

Signed-off-by: Stefan Agner <stefan@agner.ch>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>