aaudio: add support for FLOAT pcm

Add to support for AUDIO_FORMAT_PCM_FLOAT.

Request AUDIO_FORMAT_PCM_FLOAT for MMAP	streams.
Change the format to 32_BIT if openWithFormat returns error
and the format is float.

Bug: 201398105
Test: The formats listed are the internal
      AudioFlinger formats:
      Test: 1=16_BIT, 3=32_BIT, 4=8_24_BIT,
            5=FLOAT, 6=24_BIT_PACKED
Change-Id: If1ce1b31746dccba82d4eb9493d16946e39720b4