Revert "net: ti cpsw ethernet: allow reading phy interface mode from DT"

This reverts commit d7559982.

It wasn't meant to be applied, commit
342b7b74 ("net: ti cpsw ethernet: set
IFCTL_A bit in MACCONTROL") was redone in such a way to make this
commit unnecessary.

Signed-off-by: David S. Miller <davem@davemloft.net>