arm: spear: x600: Add support for Micrel KSZ9031 PHY

As the old ethernet PHY is not available any more, the x600 board has
been redesigned with the Micrel KSZ9031 PHY. This patch adds support
to autodetect the PHY and configure the Micrel PHY correctly.

Signed-off-by: Stefan Roese <sr@denx.de>