The MT7621 uses a 2 bit wide configuration of the sdhci, spi, mdio, pcie,
wdt, uart2 and uart3 in the GPIO_MODE register. It was correctly done
for sdhci, spi, pcie and wdt, The same has to be done for uart3, uart2
and mdio.

Signed-off-by: Sven Eckelmann <sven@open-mesh.com>

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@46645 3c298f89-4303-0410-b956-a3cf2f4a3e73