Add an ARM-specific VirtIO MMIO device to the VExpress_GEM5_V1 platform. Change-Id: Id1e75398e039aad9d637f46f653cda9084d3d2fe Signed-off-by: Andreas Sandberg <andreas.sandberg@arm.com> Reviewed-by: Sudhanshu Jha <sudhanshu.jha@arm.com> Reviewed-by: Nikos Nikoleris <nikos.nikoleris@arm.com> Reviewed-by: Rekai Gonzalez Alberquilla <rekai.gonzalezalberquilla@arm.com> Reviewed-on: https://gem5-review.googlesource.com/2327