va: misc fixes

    va: allocator: log dmabuf and surface at pool push or pop
    
    In order to keep track of the dmabuf fds and surfaces numbers log messages are
    added at memory_release() (queue push) and prepare_buffer() (queue pop).

    va: h265dec: fix HVC1 stream format name

    va: basedec: refactor context query
    
    Context query is handled either by source and sink queries. This patch
    factors-out its handling in a common utility function.

    va: filter: use a common GParamFlags definition
    
    Instead of repeating the same code along gst_va_filter_install_properties()

    va: h264dec: remove spurious if validation
    
    The first if checks for caps, thus else doesn't need to recheck for the
    opposite.