bootcontrol: Only compile when the A/B feature is enabled

We now only compile the HAL when the A/B feature flag is set.

Change-Id: I822fe4579de86e8785dd5708e4a063311a61d060
diff --git a/Android.mk b/Android.mk
index c593c5a..957d573 100644
--- a/Android.mk
+++ b/Android.mk
@@ -1,3 +1,4 @@
+ifeq ($(AB_OTA_UPDATER),true)
 LOCAL_PATH := $(call my-dir)
 include $(CLEAR_VARS)
 LOCAL_C_INCLUDES += hardware/libhardware/include
@@ -8,3 +9,4 @@
 LOCAL_MODULE_RELATIVE_PATH := hw
 LOCAL_MODULE := bootctrl.$(TARGET_BOARD_PLATFORM)
 include $(BUILD_SHARED_LIBRARY)
+endif