rockchip: board: lion-rk3368: increase phy autonegotiation timeout

rockchip: board: lion-rk3368: increase phy autonegotiation timeout

The first dhcp command consistently fails with a timeout when
the lion-rk3368 board is connected to a Zyxel GS1100-24E
Gigabit Ethernet switch:

  ethernet@ff290000 Waiting for PHY auto negotiation to complete......... TIMEOUT !

Increasing PHY_ANEG_TIMEOUT from the default 4000 to 8000 makes the
first dhcp command work reliably.

Signed-off-by: Jakob Unterwurzacher <jakob.unterwurzacher@theobroma-systems.com>
Reviewed-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>