media: vivid: support multiplanar touch devices

The v4l2-compliance tests failed with the touch device when multiplanar was
enabled in vivid. Since it is perfectly fine to support the multiplanar API
for touch, add support for this in vivid.

Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>