ARM: imx6: DHCOM i.MX6 PDK: Convert to DM_ETH

ARM: imx6: DHCOM i.MX6 PDK: Convert to DM_ETH

Use DM_ETH instead of legacy networking.  Add VIO as a fixed regulator
to the relevant device-trees and augment the FEC node with properties
for the reset GPIO.

It should be noted that the relevant properties for the reset GPIO
already exist in the PHY node (reset-gpios, reset-delay-us,
reset-post-delay-us) but U-Boot currently ignores those and only
supports the bus-level reset properties in the FEC node
(phy-reset-gpios, phy-reset-duration, phy-reset-post-delay).

Signed-off-by: Harald Seiler <hws@denx.de>