ar71xx: Use PHY fixups for Open Mesh MR900

The delays of PHY/MAC on the MR900 are done by u-boot and OpenWrt in
different ways. u-boot only modifies the ETH_CFG of the QCA955x based on
the link speed. But OpenWrt can only modify the PHY delays based on the
link speed.

This can lead to communication problems when u-boot initializes the ETH_CFG
for a specific link speed (e.g. 10BASE-T) but then OpenWrt the sets the PHY
delays to an incompatible value.

Instead reset the ETH_CFG delay bits of the QCA955x to a specific value and
only rely on the AT803x PHY settings.

Signed-off-by: Sven Eckelmann <sven.eckelmann@open-mesh.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@49030 3c298f89-4303-0410-b956-a3cf2f4a3e73