beckham: Enable support for prebuilt audiohal

* Setting the flag excludes building the audiohal so we
  don't still end up with the arm64 variant source built
  blob at /vendor/lib64/hw/ being stock only includes arm
  version of the hal, which when shipping the prebuilt blobs,
  are the only variants overridden.

Change-Id: I66c2216e11eec39afdbde488a153fc351e691ea9

device.mk

@@ -32,6 +32,8 @@ PRODUCT_AAPT_PREF_CONFIG := 560dpi
 PRODUCT_AAPT_PREBUILT_DPI := xxxhdpi xxhdpi xhdpi hdpi
 
 # Audio
+PREBUILT_AUDIOHAL := true
+
 PRODUCT_COPY_FILES += \
     $(LOCAL_PATH)/audio/audio_effects.xml:$(TARGET_COPY_OUT_VENDOR)/etc/audio_effects.xml \
     $(LOCAL_PATH)/audio/audio_policy_configuration.xml:$(TARGET_COPY_OUT_VENDOR)/etc/audio_policy_configuration.xml \