Add support for signal blending

This enable signal blend option,stereo mode setting
from UI.

Change-Id: Ie12eedd1c3bab9650804c6f2bc1037b3c3d0e436

helium/radio_helium_hal.c

@@ -1423,7 +1423,10 @@ static int set_fm_ctrl(int cmd, int val)
         hal->radio->recv_conf.band_low_limit = val;
         break;
     case HCI_FM_HELIUM_AUDIO_MODE:
-        hal->radio->stereo_mode.stereo_mode = ~val;
+        hal->radio->stereo_mode.stereo_mode = (char)val ? 0:1;
+        hal->radio->stereo_mode.sig_blend  = 1;
+        hal->radio->stereo_mode.intf_blend = 0;
+        hal->radio->stereo_mode.most_switch =0;
         hci_set_fm_stereo_mode_req(&hal->radio->stereo_mode);
         break;
     case HCI_FM_HELIUM_RIVA_ACCS_ADDR: