Adds a new WOV arbiter component and multi-KPB topology to support three
simultaneous wake-word detectors sharing a single DMIC, with exclusive
host PCM drain arbitration when any keyword fires.

New component: src/audio/wov_arbiter/
- 3 input pins (one per KPB host-sink), 1 output pin (to host copier)
- AMS subscriber for AMS_WOV_DETECT_MSG_UUID: activates the triggering
  slot and broadcasts WOV_CTRL PAUSE to sibling detectors
- On trigger(STOP): deactivates and broadcasts WOV_CTRL RESUME so all
  detectors return to listening
- Idle inputs are silently drained to prevent buffer stalls
- UUID 4a5b6c7d-8e9f-4a1b-2c3d-4e5f60718293 registered in uuid-registry

AMS additions (ams_msg.h):
- AMS_WOV_DETECT_MSG_UUID: detector -> arbiter on keyword detect
- AMS_WOV_CTRL_MSG_UUID:   arbiter -> detectors for pause/resume control

detect_test extensions:
- IPC4_DETECT_TEST_SET_WOV_SLOT large-config param assigns a slot id (0-2)
- On detection: also sends AMS_WOV_DETECT_MSG_UUID with slot_id to arbiter
- AMS consumer for WOV_CTRL: sets paused flag; copy() drains buffer
  without running the detector when paused
- The existing energy-threshold detector fires on a hand clap, making
  detect_test a ready-to-use lab test stub for this topology

Topology: tools/topology/topology2/platform/intel/dmic-wov-multi.conf
- Pipeline 100 (Core 0): DMIC Copier -> Mixin (fan-out to 3 Mixouts)
- Pipelines 101-102 (Core 0): Mixout -> KPB -> detect_test (slots 0-1)
- Pipeline 103 (Core 1): Mixout -> KPB -> detect_test (slot 2)
- Pipeline 104 (Core 0): WOV Arbiter -> Host Copier (single PCM stream)
- KPB output_pin_binding: pin 0 -> detector (sel_sink),
                          pin 1 -> arbiter (host_sink)

Requires: CONFIG_COMP_WOV_ARBITER, CONFIG_COMP_KPB, CONFIG_COMP_MIXIN_MIXOUT,
          CONFIG_AMS, CONFIG_COMP_KWD_DETECT

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Adds a new lightweight vad_gate module that inserts between the DMIC
copier and the Mixin fan-out in the multi-WOV capture pipeline.

The gate runs a first-order IIR energy estimator on each audio frame
(same pattern as detect_test.c's activation tracker) and manages two
states:

  SPEECH  — voice onset detected (onset_frames consecutive frames above
             threshold); audio is passed through to the Mixin → KPB →
             WOV chain which begins buffering.

  SILENCE — energy drops for hangover_frames consecutive frames; the
             gate drains its DMIC input to prevent DAI DMA stall but
             returns PPL_STATUS_PATH_STOP so the downstream Mixin and
             all three KPB/WOV pipelines idle without consuming CPU.

Tunable at runtime via IPC4 SET_LARGE_CONFIG (threshold, onset_frames,
hangover_frames, energy_shift).

Changes:
  - src/audio/vad_gate/vad_gate.c        — new component
  - src/audio/vad_gate/CMakeLists.txt
  - src/audio/vad_gate/Kconfig
  - src/include/sof/audio/vad_gate.h     — config struct + defaults
  - src/audio/Kconfig                    — CONFIG_COMP_VAD_GATE rsource
  - src/audio/CMakeLists.txt             — conditional subdirectory
  - uuid-registry.txt                    — vad_gate UUID
  - include/components/vad-gate.conf     — topology2 widget class
  - dmic-wov-multi.conf                  — pipeline 100: copier → vad-gate → mixin

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>