Add AUDIO_INPUT_FLAG_DIRECT to Audio HAL constants

This flag used to be framework only. To simplify constants
management it's better to have it defined at all layers.
Currently it is only used for MSD module but potentially
can be used for HDMI inputs.

Bug: 141273649
Test: use AOSP MSD on Pixel
      atest VtsHalAudioV6_0TargetTest

Change-Id: I19f6fdb2772878c93e41b635dc6adae83a9fecb0