CHROMIUM: virtio: video: Enhance module debugging capabilities

This patch modifies how driver checks if debug parameter is set in order
to allow enabling debugging after module have been loaded. Furthermore
command request and response logging was added.

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

BUG=None
TEST=echo 1 > /sys/module/virtio_video/parameters/debug; dmesg

Change-Id: I93fd4a848af763f30b95919ff705aab84499ca5c
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/4254045


Reviewed-by: Marcin Wojtas <mwojtas@google.com>
Commit-Queue: Bartłomiej Grzesik <bgrzesik@google.com>
Reviewed-by: Alexandre Courbot <acourbot@chromium.org>
Tested-by: Bartłomiej Grzesik <bgrzesik@google.com>