radeon/uvd: try to fix VC-1 decoding

radeon/uvd: try to fix VC-1 decoding

The DPB size calculations seem to be off; there is various random
corruption happening, even with advanced profile. Always assuming
a minimum number of references appears to fix it, similarly to
H.264. This might overallocate the DPB.  Also clean up the SPS/PPS
field setup so that it matches VC-1 specifications better.

With these changes, all advanced profile VC-1 files I could get my
hand on work fine.

Reviewed-by: Christian König <christian.koenig@amd.com>