msm: vidc: Refactor packetization of NAL format packet

Code cleanup to avoid unnecessary switch{..} blocks. Also introduce
hfi_nal_stream_format_select to prevent confusion with
hfi_nal_stream_format_supported

Change-Id: I691700292a6e26561948f484741d10fef1e79cda
Signed-off-by: Deva Ramasubramanian <dramasub@codeaurora.org>