phy: ti: gmii-sel: add support for am654x/j721e soc

TI AM654x/J721E SoCs have the same PHY interface selection mechanism for
CPSWx subsystem as TI SoCs (AM3/4/5/DRA7), but registers and bit-fields
placement is different.

This patch adds corresponding support for TI AM654x/J721E SoCs PHY
interface selection.

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