ARM: shmobile: Include all 4 GiB of memory on Lager DT Ref

Add 2GiB of DRAM at 0x1_8000_0000 to support the full 4GiB
of Lager system memory in case of DT Reference.
Signed-off-by: NMagnus Damm <damm@opensource.se>
Signed-off-by: NSimon Horman <horms+renesas@verge.net.au>

arch/arm/boot/dts/r8a7790-lager-reference.dts

@@ -25,6 +25,11 @@
 		reg = <0 0x40000000 0 0x80000000>;
 	};
 
+	memory@180000000 {
+		device_type = "memory";
+		reg = <1 0x80000000 0 0x80000000>;
+	};
+
 	lbsc {
 		#address-cells = <1>;
 		#size-cells = <1>;