vc1dec: Shuffle field MVs after decoding, not before

This simplifies the code since copying MVs to the reference is not needed
anymore (and maybe something about fixing artifacts).

Also remove the unused mv_f_last.

Fixes a small number of artifacts in black_screen_VC-1.mkv
and several more artifacts in other videos.

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Redesign the intensity compensation

Use the intensity-compensated reference frame for subsequent
fields/B-frames.

Since we currently don't change the reference frame we have to
maintain lookup tables for intensity compensation in the following
dependent frames.

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Implement intensity compensation for vc1_interp_mc()

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1: Use shuffled use_ic instead of equally shuffled mv_mode

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Drop old use_ic code from vc1_b_mc

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Fix doxy for vc1_mc_4mv_chroma4()

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Handle top and bottom blocks in vc1_mc_4mv_chroma4() differently if needed

Now it can use different references for those blocks and even use
averaging.

This fixes several chroma artifacts in several videos.

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Match addressing between compensation and MC in vc1_mc_4mv_chroma4

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Fix mixed field/frame intensity compensation

Signed-off-by: Martin Storsjö <martin@martin.st>
vc1dec: Remove interlaced warning

Also add a note about the feature in the changelog.

Signed-off-by: Martin Storsjö <martin@martin.st>