Use audio_format_t and audio_channel_mask_t in AudioPolicy

Based on:
https://github.com/CyanogenMod/android_hardware_libhardware_legacy/commit/5082dbeb19e37883230510129c94336063a4f91c
https://github.com/CyanogenMod/android_hardware_libhardware_legacy/commit/2c3d2379ee6eadb32b63bf6de538cfd6487e8e20

From above commits:

Also remove unnecessary default parameters

Also:
- use %x format for logging channel masks
- use AUDIO_CHANNEL_IN_* constants from system/audio.h instead of AudioSystemLegacy.h symbols
- remove redundant casts
- use "channelMask" instead of "channels" to avoid possible confusion with channel counts

Change-Id: I65d8b2cf8b085151194b0a1fd486bd669c1e5e70