remoteproc: Add support for vringh (Host vrings)

remoteproc: Add support for vringh (Host vrings)

Add functions for creating, deleting and kicking host-side virtio rings.

The host ring is not integrated with virtiqueues and cannot be managed
through virtio-config. Remoteproc must export functions for handling the
host-side virtio rings.

The functions rproc_virtio_get_vringh(), rproc_virtio_del_vringh(),
rproc_virtio_kick_vringh() are added to remoteproc_virtio.c. The
existing functions rproc_vq_interrupt() and rproc_virtio_find_vqs()
are updated to handle the new vhost rings.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
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>