2e: Introduce MtkInCallService

* My attempt at fixing in call gain control on MediaTek devices.
* It attempts to replicate what the stock MediaTek framework does
  when controlling the volume of the earpiece speaker, since MTK's
  audio HAL is not able to set the gain of the speaker from the
  values sent by AOSP framework.

Signed-off-by: bengris32 <bengris32@protonmail.ch>