dt-bindings: memory-controller: Add K3 AM64 DDRSS compatible

Update the k3-ddrss DT binding document to include compatible
for k3,am64-ddrss.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
diff --git a/doc/device-tree-bindings/memory-controller/k3-j721e-ddrss.txt b/doc/device-tree-bindings/memory-controller/k3-j721e-ddrss.txt
index 873a0e7..c4cf26e 100644
--- a/doc/device-tree-bindings/memory-controller/k3-j721e-ddrss.txt
+++ b/doc/device-tree-bindings/memory-controller/k3-j721e-ddrss.txt
@@ -9,7 +9,8 @@
 ==================
 Required properties:
 --------------------
-- compatible:		Shall be: "ti,j721e-ddrss"
+- compatible:		Shall be: "ti,j721e-ddrss" for j721e, j7200
+				  "ti,am64-ddrss" for am642
 - reg-names 		cfg - Map the controller configuration region
 			ctrl_mmr_lp4 - Map LP4 register region in ctrl mmr
 - reg:			Contains the register map per reg-names.