Add updatable_apex.mk

The product abstracts configs that need to be set to support updating of
APEXes.

Bug: 130418467
Test: m
Test: adb shell getprop ro.apex.updatable in Pixel 2 and 3
Test: adb shell /system/apex/com.android.apex.cts.shim.apex exists.
Change-Id: I6a892e28daadc041bba89d22b8318d146b578098
diff --git a/shared/device.mk b/shared/device.mk
index c41ff13..bf1abd7 100644
--- a/shared/device.mk
+++ b/shared/device.mk
@@ -14,6 +14,9 @@
 # limitations under the License.
 #
 
+# Enable updating of APEXes
+$(call inherit-product, $(SRC_TARGET_DIR)/product/updatable_apex.mk)
+
 PRODUCT_COPY_FILES += device/google/cuttlefish_kernel/4.14-x86_64/kernel:kernel
 
 PRODUCT_SHIPPING_API_LEVEL := 29
@@ -360,7 +363,3 @@
 
 # Host packages to install
 PRODUCT_HOST_PACKAGES += socket_forward_proxy socket_vsock_proxy
-
-# cuttlefish supports updating of APEXes
-PRODUCT_PROPERTY_OVERRIDES += \
-    ro.apex.updatable=true