videoconvert & videoscale: allow passthrough ENCODED format
Videoconvert & videoscale support passthrough, but their caps don't allow ENCODED format to be passed through it. This creates a situation where both source element and sink element can use accelerated buffer, but these 2 elements prevent it from being used.
This MR opens up these elements' template caps to allow ENCODED format in "ANY" feature. However, as "ANY" feature is a superset of sysmem feature, special care is given in their _transform_caps functions to prevent ENCODED format to be used with sysmem feature.