media: vicodec: add V4L2_ prefix before FWHT_VERSION and FWHT_FL_*

The FWHT stateless 'uAPI' was staging and marked explicitly in the
V4L2 specification that it will change and is unstable.
Note that these control IDs were never exported as a public API,
they were only defined at the driver's code.

While not too late, let's rename them is preparation for promoting
the stateless FWHT codec API as a public API.

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