ARM: dts: exynos: Prepare for inclusion of exynos5.dtsi in exynos5410.dtsi

Add 'sromc' label to SROM memory controller in common exynos5.dtsi so it
can be referenced by inheriting DTSI.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>
Tested-by: Javier Martinez Canillas <javier@osg.samsung.com>

arch/arm/boot/dts/exynos5.dtsi

@@ -35,7 +35,7 @@
 		reg = <0x10000000 0x100>;
 	};
 
-	memory-controller@12250000 {
+	sromc: memory-controller@12250000 {
 		compatible = "samsung,exynos4210-srom";
 		reg = <0x12250000 0x14>;
 	};