remoteproc: support virtio config space.

Support virtio configuration space and device status. The virtio
device can now access the resource table in shared memory.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Acked-by: Ido Yariv <ido@wizery.com>
[rebase and style changes]
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>