drivers: net: cpsw-phy-sel: add support to configure rgmii internal delay

Add support to enable CPSW RGMII internal delay (id mode) bits
when rgmii internal delay is configured in phy.

Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>