To simplify writing native VirtIO drivers for Genode add helper classes
representing VirtIO device and queue. The queue implementation should
be platform independant. The device abstraction however is closely tied
to the VirtIO transport being used (PCI/MMIO). Both PCI and MMIO
implementations expose the same public API so the actual driver logic
should be the same regardless of which transport is used.
Its also important to note that the PCI version of Virtio::Device
currently does not support MSI-X interrupts. Unfortunately my kowledge
about PCI bus is very limited and my main area of interest was to get
VirtIO drivers working on virt_qemu ARM/Aarch64 platform. As such all
the VirtIO drivers I plan to submit will work with PCI bus, but might
not use some extended capabilities.
Ref #3825
