h265parser: refactoring some methods to be more like h264parser

Submitted by m][sko

Link to original bug (#769717)

Description

I think we should refactor h265parser's methods to be more like h264parser
for example gst_h265_parse_process_nal, gst_h265_parse_handle_frame

in gst_h265_parse_handle_frame
there is part with "no SPS/PPS yet, nal Type: %d %s, Size: %u will be dropped"
that is really not good
h264parser don't have something like this