CHROMIUM: video: virtio: Defer virtio video init work

This patch defers partial initialization of virtio video device to global
kernel workqueue in order to reduce probe execution time whenever
CMD_QUERY_CAPABILITY fails to respond (eg. hypervisor backend failure).
Initialization of V4L2 Device was moved to a deferred function to prevent
usage of the device before full initialization is finished. For this reason
v4l2_err no longer could be used for printing and was replaced with
dev_err. Furthermore a switch to video_register_device_no_warn to suppress
index duplication warning.

Signed-off-by: Bartłomiej Grzesik <bgrzesik@google.com>

BUG=b:235763012
TEST=Request sign off on Chromebook during VM boot

Change-Id: I7aa2a92810e1b920fee8ba104a8f9c7f401ec00d
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4177375


Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Marcin Wojtas <mwojtas@google.com>
Tested-by: Hubert Mazur <hmazur@google.com>
Commit-Queue: Bartłomiej Grzesik <bgrzesik@google.com>
Signed-off-by: Slawomir Rosek <srosek@google.com>