realtek: evaluate pcs-handle instead of sds property

realtek: evaluate pcs-handle instead of sds property

In the Realtek dts the pcs-handle property at the switch port is the
successor of the sds property at the phy. Rearrange the MDIO and DSA
driver so they always look at the new attribute.

Remark! This code can be dropped completely if the new PCS driver
is fully featured. But this will take some time.

Signed-off-by: Markus Stockhausen <markus.stockhausen@gmx.de>
Link: https://github.com/openwrt/openwrt/pull/20148
Signed-off-by: Robert Marko <robimarko@gmail.com>