vah264enc: Misc updates
gst_plugins_cache.json: Update va plugins.
* Update conditionally-available attribute in vah264enc properties.
* Update GstVaFeature usage.
* Update GstVaEncoderRatecontrol usage.
* Update vapostproc classification.
* Add `add-borders` property in vapostproc.
vah264enc: Use GstVaFeature enum for enabling MBBRC.
GstVaFeature is a common enumeration for auto/disabled/enabled kind of
property setting.
vah264enc: Move rate-control enum to encoder class helper.
Since it's a common enumeration used, as user setting property, for
most of codecs.
vah264enc: Add device-path property.