arm64: dts: Add a virtio disk to the RTSM motherboard

Describe the virtio device so we can mount disk images in the simulator.

[Reduced the size of the region based on feedback from review -- broonie]
Signed-off-by: Mark Hambleton <mahamble@broadcom.com>
Signed-off-by: Mark Brown <broonie@linaro.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/boot/dts/rtsm_ve-motherboard.dtsi

@@ -183,6 +183,12 @@ clcd@1f0000 {
 				clocks = <&v2m_oscclk1>, <&v2m_clk24mhz>;
 				clock-names = "clcdclk", "apb_pclk";
 			};
+
+			virtio_block@0130000 {
+				compatible = "virtio,mmio";
+				reg = <0x130000 0x200>;
+				interrupts = <42>;
+			};
 		};
 
 		v2m_fixed_3v3: fixedregulator@0 {