Limit input routing to config_enableInputRouting

Add config_enableInputRouting to only enable input routing on
certain devices.

Bug: b/441643494
Test: atest AudioSwitchControllerTest
Flag: com.android.media.flags.enable_audio_input_device_routing_and_volume_control

Change-Id: I11e0e989756d0284c5230c4444169a8271c30dbe