vah264enc: Avoid reopen encoder or renegotiate.

vah264enc: Avoid reopen encoder or renegotiate.

If parameters remain similar enough to avoid either encoder reopening
or downstream renegotiation, avoid it.

This is going to be useful for dynamic parameters setting.

To check if the stream parameters changed, so the internal encoder has
to be closed and opened again, are required two steps:

1. If input caps, profile, chroma or rate control mode have changed.
2. If any of the calculated variables and element properties have
   changed.

Later on, only if the output caps also changed, the pipeline
is renegotiated.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/2466>