dev: Fix reset of virtio devices

dev: Fix reset of virtio devices

The VirtualQueue reset was just resetting the queue address but
it was not touching other cached state and its associated
ring buffers (used and avail)

Change-Id: I55cc767d791825899d62c4cd88b84809527f3f22
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/39701
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>