Revert "Move H264/QPEL specific asm from dsputil.asm to h264_qpel_*.asm."

This reverts commit f90ff772e7e35b4923c2de429d1fab9f2569b568.

The code should be put back in h264_qpel_8bit.asm, but unfortunately
it is unconditionally used from dsputil_mmx.c since 71155d7.
lls: #ifndef --> #if in FF_API_ version guard
lls: Do not return from void functions
flvdec: Don't read the VP6 header byte when setting codec type based on metadata

This header byte is only present when actually reading a VP6 frame,
not when reading the codec type field in the metadata. This
potential bug has been present since 5b54a90c.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
flvdec: Check the return value of a malloc

The callers of this function can't report errors sanely. If this
one malloc fails, don't write the extradata byte, make sure we
try to malloc it the next time we're called instead, and make sure
we still consume the input data byte.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>