db845c: Add Inherit-product for updatable_apex

Recent changes caused the db845c to stop booting successfully,
and it was narrowed down to boringssl failures caused by us
missing the line to inherit updatable_apex.

This patch adds the line, and gets the board to boot again.

Change-Id: Ia56a4dc5eba92b6b044880782624b967b1baeb69
Signed-off-by: John Stultz <john.stultz@linaro.org>

device-common.mk

@@ -14,6 +14,9 @@
 # limitations under the License.
 #
 
+# Enable updating of APEXes
+$(call inherit-product, $(SRC_TARGET_DIR)/product/updatable_apex.mk)
+
 # Device overlay
 DEVICE_PACKAGE_OVERLAYS := $(LOCAL_PATH)/overlay