Use channel mask instead of channel count for track creation

Record and playback objects (resp AudioRecord and AudioTrack)
are created using a channel mask, but this information is lost
in the mixer because only the channel count is known to
AudioFlinger. A channel count can always be derived from a
channel mask.

The change consists in:
- disambiguiting variable names for channel masks and counts
- passing the mask information from the client to AudioFlinger
 and the mixer.
- when using the DIRECT ouput, only verifying the format of
 the track is compatible with the output's for PCM.

Change-Id: I50d87bfb7d7afcabdf5f12d4ab75ef3a54132c0e
diff --git a/services/audioflinger/AudioMixer.h b/services/audioflinger/AudioMixer.h
index 88408a7..75c9170 100644
--- a/services/audioflinger/AudioMixer.h
+++ b/services/audioflinger/AudioMixer.h
@@ -61,7 +61,7 @@
 
         // set Parameter names
         // for target TRACK
-        CHANNEL_COUNT   = 0x4000,
+        CHANNEL_MASK    = 0x4000,
         FORMAT          = 0x4001,
         MAIN_BUFFER     = 0x4002,
         AUX_BUFFER      = 0x4003,
@@ -150,6 +150,7 @@
         uint8_t     enabled      : 1;
         uint8_t     reserved0    : 3;
         uint8_t     format;
+        uint32_t    channelMask;
 
         AudioBufferProvider*                bufferProvider;
         mutable AudioBufferProvider::Buffer buffer;