caif_virtio: Introduce caif over virtio

caif_virtio: Introduce caif over virtio

Add the the Virtio shared memory driver for STE Modems.
caif_virtio is implemented utilizing the virtio framework
for data transport and is managed with the remoteproc frameworks.

The Virtio queue is used for transmitting data to the modem, and
the new vringh implementation is receiving data over the vring.

Signed-off-by: Vikram ARV <vikram.arv@stericsson.com>
Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
cc: David S. Miller <davem@davemloft.net>
cc: Ohad Ben-Cohen <ohad@wizery.com>
cc: Rusty Russell <rusty@rustcorp.com.au>
cc: Ido Yariv <ido@wizery.com>
cc: Erwan Yvin <erwan.yvin@stericsson.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>