port dashcamd: hardware-encoded MP4 dashcam

VisionIPC frames from camerad → OMX H.264 hardware encoder → 3-min MP4
segments + SRT GPS subtitles in /data/media/0/videos/<trip>/. Manages
its own trip lifecycle (WAITING/RECORDING/IDLE_TIMEOUT) and writes
DashcamState/DashcamFrames memory params for the UI's Status window.
Honors DashcamShutdown for graceful close before power-off.

Files added:
- selfdrive/clearpilot/dashcamd.cc + SConscript

Files modified:
- selfdrive/frogpilot/screenrecorder/omx_encoder.{cc,h}: ported broken's
  version, which adds encode_frame_nv12() (direct NV12 input from camerad,
  alongside the existing encode_frame_rgba used by the disabled screen
  recorder) and simplifies the libyuv conversion paths to NEON-only since
  this device is aarch64.
- selfdrive/SConscript: register selfdrive/clearpilot/SConscript so the
  dashcamd binary is part of the build.
- selfdrive/manager/process_config.py:
  - camerad gating driverview → always_run so dashcamd can record the
    moment ignition+drive arrives without waiting for camera startup.
  - Register dashcamd as NativeProcess gated always_run.
- system/loggerd/deleter.py:
  - MIN_BYTES 5 GB → 9 GB to leave headroom for dashcam footage.
  - delete_oldest_video(): trip-aware cleanup. Drops entire oldest trip
    dir first; if only the active trip remains, drops oldest segment
    inside it; cleans up legacy flat .mp4s too.
  - cleanup_log2(): keeps /data/log2 session logs under 4 GB total.
  - Hooked into deleter_thread: video first when out of bytes/percent;
    log2 quota check on the idle path. New code uses print(stderr) per
    the no-cloudlog rule.

Verified: built clean, manager started, dashcamd in WAITING state
(DashcamState=waiting, DashcamFrames=0), camerad running, no errors.

selfdrive/SConscript

@@ -3,4 +3,5 @@ SConscript(['controls/lib/lateral_mpc_lib/SConscript'])
 SConscript(['controls/lib/longitudinal_mpc_lib/SConscript'])
 SConscript(['locationd/SConscript'])
 SConscript(['modeld/SConscript'])
-SConscript(['ui/SConscript'])
+SConscript(['ui/SConscript'])
+SConscript(['clearpilot/SConscript'])