libx265: enable psnr reporting when requested by the user

This is similar to what is done in libx264.c

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Derek Buitenhuis <derek.buitenhuis@gmail.com>
Merge commit 'd10d1b86550d254bd1e746ed613bf6885978879c'

* commit 'd10d1b86550d254bd1e746ed613bf6885978879c':
  libx265: enable psnr reporting when requested by the user

See: 3956b12fdec5ec1b1358788a6000b78a724f76aa
Merged-by: Michael Niedermayer <michaelni@gmx.at>
avformat/flvenc: fix codec_id_text check

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>