ipq40xx: wpj428: fix missing MDIO GPIO reset and pinmux

ipq40xx: wpj428: fix missing MDIO GPIO reset and pinmux

The bootloader does not always initialize the MDIO pins before booting
Linux. E.g. on version "U-Boot 2012.07 [Chaos Calmer 15.05.1,r35193] (Jul
25 2017 - 11:36:26)" this is the case when booting automatically without
activating the U-Boot console.

Without this change, the kernel boot will complain about missing PHYs:

 libphy: ipq40xx_mdio: probed
 ar40xx c000000.ess-switch: Probe failed - Missing PHYs!
 libphy: Fixed MDIO Bus: probed

With this change it will work as expected:

 libphy: ipq40xx_mdio: probed
 ESS reset ok!
 ESS reset ok!
 libphy: Fixed MDIO Bus: probed

Ref: GH-2835
Tested-by: Fredrik Olofsson <fredrik.olofsson@anyfinetworks.com>
Signed-off-by: Leon M. George <leon@georgemail.eu>
[commit description from Fredrik, subject facelift]
Signed-off-by: Petr Štetiar <ynezz@true.cz>