audiopolicy: Never use low-latency audio for ringtones

 * If a device is under heavy load or thermal mitigation, it's
   possible for the audio thread to starve the system of resources.
   This can result in the heads-up notification taking many seconds to
   appear, or potentially miss the call entirely.
 * Force deep-buffer for all ringtones if
   AUDIO_FEATURE_DEEP_BUFFER_RINGTONE is set during compilation.

CYNGNOS-969

Change-Id: I74a07850f0140697bb121328e170a7ac5a1f5e7a
(cherry picked from commit 613cdc28)