ARM: dts: imx6ull-colibri: add phy-supply to fec

This adds the proper phy-supply to the FEC. This supply is actually
switched by a clock that is now properly stated. This has the advantage
to add a delay for that particular regulator which is needed.

Signed-off-by: Philippe Schenker <philippe.schenker@toradex.com>
Signed-off-by: Denys Drozdov <denys.drozdov@toradex.com>
Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>