hevc: do not store pcm_flag in the context

It does not need to be accessed outside of hls_coding_unit().
hevc: do not store rqt_root_cbf in the context

It does not need to be accessed outside of hls_coding_unit().
hevc: remove a redundant line

pred_mode is overwritten a few lines immediately below.
hevc: remove an unused function parameter
hevcdsp_template: templatize transquant_bypass
hevc: reduce code duplication in hls_prediction_unit()
hevc: further reduce code duplication in hls_prediction_unit()
hevc: reduce variable scope

Also, collapse the array into a scalar, since only one value is needed
at a time.
hevc: eliminate an unneeded intermediate variable
hevc: remove superfluous assignments and checks
flvenc: move metadata updates into a single function

Signed-off-by: Anton Khirnov <anton@khirnov.net>
flvenc: Send new metadata when FLAG_METADATA_UPDATED is set.

Signed-off-by: Anton Khirnov <anton@khirnov.net>