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>
Git-commit: 1bb2cbb6a5182c9be5dd162ba06986f11d2cbbc0
Git-repo: git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git


Signed-off-by: Ian Maund <imaund@codeaurora.org>