ARM: tegra: fix memory size on Beaver

Tegra30's boot ROM masks the top 1MiB of RAM. Fix the memory node in
Beaver's DT file to reflect this.
Signed-off-by: Stephen Warren <swarren@nvidia.com>

arch/arm/boot/dts/tegra30-beaver.dts

@@ -7,7 +7,7 @@ / {
 	compatible = "nvidia,beaver", "nvidia,tegra30";
 
 	memory {
-		reg = <0x80000000 0x80000000>;
+		reg = <0x80000000 0x7ff00000>;
 	};
 
 	pinmux {