InCallUI: improve in-call UI for different supported routes

On some devices, there is no earpiece route available, and the speaker
is the default audio output. To make in-call UI correctly operate on
such devices, the following changes are introduced:

* the "earpiece handset" output icon becomes hidden from the list of
  choices in the audio button if no earpiece route is supported

* if device does not support earpiece route but wired headset is
  plugged in, the "earpiece handset" output icon becomes visible
  to reflect the wired headset as an actual call audio output

* the text option of earpiece becomes hidden from choices if the
  device does not support earpiece route

* audio button is shown only if there are more than one route is
  present on the device, otherwise it stays hidden

Test:

* On devices with speaker and earpiece routes present, the audio
  button is visible and acts like a speaker toggle

* On devices with speaker and earpiece routes present and wired
  headset plugged in, the audio button is visible and acts as
  a speaker toggle

* On devices with speaker-only or earpiece-only routes present
  and wired headset plugged in, the audio button is visible and
  acts as a speaker toggle

* On devices with speaker and earpiece routes present and
  Bluetooth headset paired, the audio button is visible and acts
  as a multi-state toggle allowing user to choose Bluetooth
  (by default), speaker or handset earpiece

* On devices with speaker-only or earpiece-only routes present
  and Bluetooth headset paired, the audio button is visible and
  acts as a multi-state toggle allowing user to choose Bluetooth
  (by default) and speaker or handset earpiece

* On devices with speaker-only or earpiece-only routes present,
  the audio button is invisible

Change-Id: I9359aaaa44b89f5937cc1a7d9fbd5fe25c71133d