Bonito/Sargo supports updatable APEX

Before, updatable_apex.mk was inherited indirectly from
mainline_system.mk. Since mainline_system.mk no longer inherits
updatable_apex.mk, updatable_apex.mk is inherited directly from
device-specific mk file.

Bug: 132664085
Test: choosecombo to bonito and sargo; get_build_var TARGET_FLATTEN_APEX
shows false

Change-Id: I0a0923da157ec87bd139883e14a948466a134554
diff --git a/device-common.mk b/device-common.mk
index 34b8327..58f1800 100644
--- a/device-common.mk
+++ b/device-common.mk
@@ -21,6 +21,9 @@
 # define hardware platform
 PRODUCT_PLATFORM := sdm670
 
+# Enable updating of APEXes
+$(call inherit-product, $(SRC_TARGET_DIR)/product/updatable_apex.mk)
+
 include device/google/bonito/device-audio-mfg.mk
 include device/google/bonito/device.mk