virtio: memory access APIs

virtio 1.0 makes all memory structures LE, so
we need APIs to conditionally do a byteswap on BE
architectures.

To make it easier to check code statically,
add virtio specific types for multi-byte integers
in memory.

Add low level wrappers that do a byteswap conditionally, these will be
useful e.g. for vhost.  Add high level wrappers that
query device endian-ness and act accordingly.

Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>

diff --cc include/linux/virtio_byteorder.h
Simple merge

diff --cc include/linux/virtio_config.h
Simple merge

diff --cc include/uapi/linux/Kbuild
Simple merge

diff --cc include/uapi/linux/virtio_ring.h
Simple merge

diff --cc include/uapi/linux/virtio_types.h
Simple merge