Revert "dts: socfpga: Add DTS entry for adding the stmmac glue layer for stmmac."

This reverts commit 7e0b4cd0.

The binding changes need to be done differently as well, let's
take them through netdev, and merge the dts changes in a new
patch here.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>