net: ethernet: ti: cpsw: add support for port interface mode selection phy

Add support for port interface mode selection phy (phy-gmii-sel):
- try to request interface mode selection phy from Port DT node and fail
silently if not defined and old CONFIG_TI_CPSW_PHY_SEL driver enabled.
- use new phy if requested successfully.

Cc: Kishon Vijay Abraham I <kishon@ti.com>
Cc: Tony Lindgren <tony@atomide.com>
Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>