Convert mask types from uint32_t to enum type

This applies to the following types:

- audio_gain_mode_t;
- audio_flags_mask_t;
- audio_channel_representation_t;
- audio_channel_mask_t;
- audio_devices_t.

Enum types are distinct thus proper overloading on the type
is possible in C++. Also, assignments to enum types are
less prone to errors.

Bug: 169889714
Test: basic audio functionality
      m stagefright
      atest audiopolicy_tests
Change-Id: I42506484b1d0b0482618b7314fad4c8012a06fb4
Merged-In: I42506484b1d0b0482618b7314fad4c8012a06fb4
diff --git a/services/audioflinger/SpdifStreamOut.cpp b/services/audioflinger/SpdifStreamOut.cpp
index c7aba79..0ce5681 100644
--- a/services/audioflinger/SpdifStreamOut.cpp
+++ b/services/audioflinger/SpdifStreamOut.cpp
@@ -39,7 +39,7 @@
         , mSpdifEncoder(this, format)
         , mApplicationFormat(AUDIO_FORMAT_DEFAULT)
         , mApplicationSampleRate(0)
-        , mApplicationChannelMask(0)
+        , mApplicationChannelMask(AUDIO_CHANNEL_NONE)
 {
 }