phy: ti: gmii-sel: Add support for configuring CPSW5G ports in SGMII mode

commit 7587de8f2efc45d806a1e3e467c4d23401eac37f from
git://git.ti.com/ti-linux-kernel/ti-linux-kernel.git

CPSW5G ports on J7200 support SGMII mode. Add support to the phy-gmii-sel
driver to configure the CPSW5G ports in SGMII mode.

Signed-off-by: Siddharth Vadapalli <s-vadapalli@ti.com>
Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Signed-off-by: Xulin Sun <xulin.sun@windriver.com>