lavc: add a property for marking codecs that support frame reordering
codec_desc: fix some typos in long codec names

The rv20 typo spotted by Hendrik Leppkes <h.leppkes@gmail.com>
hevc: eliminate an unnecessary array

We do not need to store the value of the split flag.
hevc: simplify splitting the transform tree blocks
hevc: do not store the transform inter_split flag in the context

It does not need to be preserved.
hevc: eliminate unnecessary cbf_c{b,r} arrays

They are replaced by passing additional parameters to the transform
functions.
hevc: eliminate the last element from TransformTree

Replace it by passing an additional parameter to transform_unit()