arm: dts: k3-am642: Add ddr node

Introduce ddr node for am642 needed for all ddr configurations.

Also, introduce the 1600MTs DDR4 configuration that is supported on the
am642-evm.
Signed-off-by: NDave Gerlach <d-gerlach@ti.com>

arch/arm/dts/k3-am642-r5-evm.dts

@@ -6,6 +6,8 @@
 /dts-v1/;
 
 #include "k3-am642.dtsi"
+#include "k3-am64-evm-ddr4-1600MTs.dtsi"
+#include "k3-am64-ddr.dtsi"
 
 / {
 	chosen {