checkasm: hevc: Iterate over features first, then over bitdepths

This avoids listing the same feature multiple times in the
test output. Previously the output contained something like this:

SSE2:
 - hevc_mc.qpel              [OK]
 - hevc_mc.epel              [OK]
 - hevc_mc.unweighted_pred   [OK]
 - hevc_mc.qpel              [OK]
 - hevc_mc.epel              [OK]
 - hevc_mc.unweighted_pred   [OK]

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