Instead of using a combination of bitreader and -writer for copying data,
one can byte-align the (obsolete and removed) bitreader to improve performance.
With the right alignment one can even use memcpy. The right alignment
normally exists for CABAC and hence for H.265 in general.
For aligned data this reduced the time to copy the slicedata from
776520 decicycles to 33889 with 262144 runs and a 6.5mb/s H.264 video.
For unaligned data the number went down from 279196 to 97739 decicycles.
Signed-off-by: Mark Thompson <sw@jkqxz.net>