hal: Provide support to enable/disable EC/NS in BT

Currently during a SCO connection ECNS module in ADSP
is disabled by default. Some BT headsets have built-in
support for echo cancellation and noise reduction and
therefore do not require the same to be done again.
Select BT_SCO devices with ECNS modules enabled when
setParameters() is called with NREC=on.

Change-Id: I8bc37358a4510de7112d5247efbd5d3d7420fe43
diff --git a/hal/audio_hw.c b/hal/audio_hw.c
index c394391..31aa222 100644
--- a/hal/audio_hw.c
+++ b/hal/audio_hw.c
@@ -2672,9 +2672,7 @@
 
     err = str_parms_get_str(parms, AUDIO_PARAMETER_KEY_BT_NREC, value, sizeof(value));
     if (err >= 0) {
-        /* When set to false, HAL should disable EC and NS
-         * But it is currently not supported.
-         */
+        /* When set to false, HAL should disable EC and NS */
         if (strcmp(value, AUDIO_PARAMETER_VALUE_ON) == 0)
             adev->bluetooth_nrec = true;
         else