net: ti: cpsw: fix mac tx internal delay for rgmii-rxid mode

Now TI CPSW driver will disable MAC TX internal delay for PHY interface
mode "rgmii-rxid" which is incorrect.

Hence, fix it by keeping default value (enabled) for MAC TX internal delay
when "rgmii-rxid" interface mode is selected.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>