avformat/hlsenc: add hls encrypt options

refer to:
https://git.libav.org/?p=libav.git;a=commitdiff;h=0a4b9d0ccd10b3c39105f99bd320f696f69a75a2


add hls encrypt options looks like libav's libavformat/hlsenc.c

Reviewed-by: Moritz Barsnick <barsnick@gmx.net>
Signed-off-by: Steven Liu <lq@chinaffmpeg.org>