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>

Documentation/devicetree/bindings/phy/ti-phy-gmii-sel.txt

@@ -40,6 +40,7 @@ Required properties:
 			  "ti,dra7xx-phy-gmii-sel" for dra7xx/am57xx platform
 			  "ti,am43xx-phy-gmii-sel" for am43xx platform
 			  "ti,dm814-phy-gmii-sel" for dm814x platform
+			  "ti,am654-phy-gmii-sel" for AM654x/J721E platform
 - reg			: Address and length of the register set for the device
 - #phy-cells		: must be 2.
 			  cell 1 - CPSW port number (starting from 1)