hal: update combo device handling

If the wired headset/headphone/line devices are handled by
a different backend than speaker/earpiece devices, the combo
devices such as speaker+headphones can be split into individual
devices and enabled/disabled independently.

Conflicts:
	hal/msm8916/platform.c
	hal/msm8974/platform.c

Change-Id: I30e90f398ef204d106b5d8dac8fba166583bdbc8
diff --git a/hal/msm8974/platform.h b/hal/msm8974/platform.h
index be5160a..b56c40e 100644
--- a/hal/msm8974/platform.h
+++ b/hal/msm8974/platform.h
@@ -182,7 +182,12 @@
 
 enum {
     DEFAULT_CODEC_BACKEND,
+    SLIMBUS_0_RX = DEFAULT_CODEC_BACKEND,
     HEADPHONE_44_1_BACKEND,
+    SLIMBUS_5_RX = HEADPHONE_44_1_BACKEND,
+    HEADPHONE_BACKEND,
+    SLIMBUS_6_RX = HEADPHONE_BACKEND,
+    HDMI_RX_BACKEND,
     MAX_CODEC_BACKENDS
 };