Create separate build targets for utility/ in APM

This clarifies the dependencies of utility/ a lot (spoiler:
there are very few) and makes it easier to separate the build
targets for aecm and aec2.

Bug: webrtc:9488
Change-Id: If916f86e80c19d1b650d0908fbe8343ea7c47bd7
Reviewed-on: https://webrtc-review.googlesource.com/87141
Reviewed-by: Alex Loiko <aleloi@webrtc.org>
Commit-Queue: Sam Zackrisson <saza@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23860}

modules/audio_processing/utility/delay_estimator_unittest.cc

@@ -33,8 +33,8 @@ const size_t kSizeEnable = sizeof(kEnable) / sizeof(*kEnable);
 class DelayEstimatorTest : public ::testing::Test {
  protected:
   DelayEstimatorTest();
-  virtual void SetUp();
-  virtual void TearDown();
+  void SetUp() override;
+  void TearDown() override;
 
   void Init();
   void InitBinary();