bktr: Add missing includes for av_gettime()

This is necessary after the old av_gettime in libavformat was
dropped.

Signed-off-by: Martin Storsjö <martin@martin.st>
x86: Remove win64 xmm clobbering wrappers for the now removed avcodec_encode_video function

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