hevc: fix race condition in max_ra/seq_decode.

These variables are shared between frame threads, but they are updated
post-setup_finished() if a EOB/EOS slice type occurs. Moving the EOB/EOS
slices to the next frame thread instance (by parsing them leading into
the next picture instead of trailing behind the last picture) effectively
prevents this race condition.

This fixes tsan failures on hevc-conformance-NoOutPrior_A_Qualcomm_1.
