Add AudioChannelMask to Framework SAIDL definition

Framework SAIDL used to use 'int' for the channel mask
type. To help finding all the places where channel masks
are used, add a designated type. Currently it's an enum,
but it will be changed to a more extendable type soon (see
the bug and the plan document).

Bug: 188932434
Test: m
Change-Id: If2d958fcc92b8e549493d3fa83b35c12dcda2ccc
diff --git a/media/libaudioclient/Android.bp b/media/libaudioclient/Android.bp
index 37e68bb..4652a18 100644
--- a/media/libaudioclient/Android.bp
+++ b/media/libaudioclient/Android.bp
@@ -302,6 +302,7 @@
     local_include_dir: "aidl",
     srcs: [
         "aidl/android/media/AudioAttributesInternal.aidl",
+        "aidl/android/media/AudioChannelMask.aidl",
         "aidl/android/media/AudioClient.aidl",
         "aidl/android/media/AudioConfig.aidl",
         "aidl/android/media/AudioConfigBase.aidl",