CRAS: support style transfer for ALSA_LOOPBACK

In the tast test cras_noise_cancellation.go, we're using alsa loopback
to generate microphone input and trigger the invocation of the effect.
Before this change, style transfer has been updated to support internal
mic only, which resulted in testing with unexpected effect. This change
makes style transfer not only support internal mic but also alsa
loopback to make the test with correct effect.

BUG=b:347911392
TEST=tast run ${D} audio.CrasNoiseCancellation.aec_nc_ast

Change-Id: I418f23e6a8eb372d455e3b99a3955d54008e3fd8
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/adhd/+/5633068
Tested-by: Cranel W <[email protected]>
Reviewed-by: Li-Yu Yu <[email protected]>
Commit-Queue: Cranel W <[email protected]>

Author: Cranel W

cras/src/server/cras_alsa_common_io.c

@@ -71,10 +71,11 @@ enum CRAS_NC_PROVIDER cras_alsa_common_get_nc_providers(
     struct cras_use_case_mgr* ucm,
     const struct cras_ionode* node) {
   enum CRAS_NC_PROVIDER provider = 0;
-  if (node->type == CRAS_NODE_TYPE_MIC &&
-      (node->position == NODE_POSITION_INTERNAL ||
-       node->position == NODE_POSITION_FRONT) &&
-      cras_system_get_style_transfer_supported()) {
+  if ((node->type == CRAS_NODE_TYPE_ALSA_LOOPBACK ||  // Alsa loopback.
+       (node->type == CRAS_NODE_TYPE_MIC &&           // Internal mic.
+        (node->position == NODE_POSITION_INTERNAL ||
+         node->position == NODE_POSITION_FRONT))) &&
+      cras_system_get_style_transfer_supported()) {  // Supportness.
     provider |= CRAS_NC_PROVIDER_AST;
   }
   if (ucm && cras_system_get_dsp_noise_cancellation_supported() &&