encoder: h264: submit SEI buffering_period() and picture_timing() messages for CBR...

encoder: h264: submit SEI buffering_period() and picture_timing() messages for CBR mode

One buffering_period() SEI message shall be present in every IDR access unit
when NalHrdBpPresentFlag is inferred to be equal to 1. This is the case when we
use a non-CQP mode, e.g. CBR. In other words, when
nal_hrd_parameters_present_flag is set to 1.

One picture_timing() SEI messages shall be present in every access unit
if CpbDpbDelaysPresentFlag is equal to 1 or pic_struct_present_flag is equal to 1

https://bugzilla.gnome.org/show_bug.cgi?id=722734
https://bugzilla.gnome.org/show_bug.cgi?id=751831

Signed-off-by: Sreerenj Balachandran <sreerenj.balachandran@intel.com>