avformat/hlsenc: support mkdir_p for use_localtime_mkdir

avformat/hlsenc: support mkdir_p for use_localtime_mkdir

when use use_localtime_mkdir to create multi level dir,
ffmpeg give error message:
ffmpeg -re -i ~/Movies/objectC/facebook.mp4 -c copy -use_localtime 1
 -use_localtime_mkdir 1 -hls_segment_filename '%Y%m%d/file-%Y%m%d/%s.ts'
out.m3u8
error message:
Could not create directory 20160926/file-20160926 with use_localtime_mkdir
add mkdir_p for support the multi level dir

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Tested-by: Zuo Genyu <1515161258@qq.com> (Windows)
Signed-off-by: Steven Liu <lingjiujianke@gmail.com>