kvm tools: virtio: remove hardcoded assumptions about guest page size

virtio-based PCI devices deal only with 4k memory granules, making
direct use of the VIRTIO_PCI_VRING_ALIGN and VIRTIO_PCI_QUEUE_ADDR_SHIFT
constants when initialising the virtqueues for a device.

For MMIO-based devices, the guest page size is arbitrary and may differ
from that of the host (this is the case on AArch64, where both 4k and
64k pages are supported).

This patch fixes the virtio drivers to honour the guest page size passed
when configuring the virtio device and align the virtqueues accordingly.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>