v4l2_stateful_decoder: Make H264 functions static

This CL makes privately used functions static to avoid future name
collisions.

BUG=b:227248846
TEST=tast run ${DUT} video.PlatformDecoding.v4l2_h264*

Change-Id: Ic55f93a3a02453daac40634b81dc6979c65f8381
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/drm-tests/+/3566877
Reviewed-by: Fritz Koenig <frkoenig@chromium.org>
Tested-by: Nathan Hebert <nhebert@chromium.org>
Commit-Queue: Nathan Hebert <nhebert@chromium.org>
2 files changed