flounder: switch all products to inherit from core_64_bit.mk

Inherit from core_64_bit.mk to pick up the standard 64-bit
configuration.

Change-Id: I2970c8966d921e7dddf447c1133aed878e55fd50
diff --git a/product.mk b/product.mk
index f663432..ddf599d 100644
--- a/product.mk
+++ b/product.mk
@@ -19,4 +19,5 @@
 
 PRODUCT_RUNTIMES := runtime_libart_default
 
+$(call inherit-product, $(SRC_TARGET_DIR)/product/core_64_bit.mk)
 $(call inherit-product, device/htc/flounder/device.mk)