Merged two similar functions to reduce duplication

Function encode_rtc_frame_internal() and encode_frame_internal() only
differed by a couple of speed features, this commit relocation those
difference into the setup of speed features and merged two functions
into one to remove duplication.

It also fixed a subtle bug super_fast_rtc was used before it was
initialized.

Change-Id: I234a5a1d11a4450930e5b4943dbab434208d5030