dt-bindings: 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 compatible strings to enable support for TI
AM654x/J721E SoCs.

Signed-off-by: Grygorii Strashko <grygorii.strashko@ti.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>