audio policy: add hw hotword flag for inputs

Audio input profiles can indicate flag AUDIO_INPUT_FLAG_HW_HOTWORD
meaning they allow capture from the same source as HW hotword
detection.

When a client requests capture with this flag, the policy will
try to find an input profile matching this request first and
fallback to a regular input if not found.

Bug: 17575019.
Change-Id: Ia463211597d7fa363527d776389f2257f0ced9a2