board/BuR: fix pinmux for MII Ethernet Interface

The lines COL (collision detect) and CRS (carrier sense) needs to be connected
and muxed to the CPSW MAC for a proper function in half-duplex Mode of the
interface.

Signed-off-by: Hannes Petermaier <oe5hpm@oevsv.at>
Cc: Tom Rini <trini@ti.com>