ARM: dts: am335x-evm: fix number of cpsw

am335x-evm has only one CPSW external port physically wired, but DT defines
2 ext. ports. As result, PHY connection failure reported for the second
ext. port.

Update DT to reflect am335x-evm board HW configuration, and, while here,
switch to use phy-handle instead of phy_id.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>