Revert "ar71xx: Allow to set the RXDV, RXD, TXD, TXE delays for QCA955x"

The default delays RXD 3. RDV 3, TXD 0, TXE 0 doesn't seem to work for some
boards. These boards depend on the preset values of u-boot which may
differ.

This reverts commit f2d4bb96b62512caa161dcc2867c91692fb16a38.

Signed-off-by: Sven Eckelmann <sven.eckelmann@open-mesh.com>
git-svn-id: svn://svn.openwrt.org/openwrt/trunk@49071 3c298f89-4303-0410-b956-a3cf2f4a3e73