Use board config variable BOARD_WIDEVINE_OEMCRYPTO_LEVEL

Instead of grepping out the oemcrypto level from PRODUCT_PACKAGES, which
is very fragile.

Change-Id: I1ac5b8ace25dd4798d3383304f01496f12193526

proprietary/cryptoPlugin/decrypt-core.mk

@@ -3,10 +3,14 @@
 #  Widevine wvm static library.  Sets up includes and defines the core libraries
 #  required.
 #
-include $(TOP)/vendor/widevine/proprietary/wvm/common.mk
+include vendor/widevine/proprietary/wvm/common.mk
+
+ifndef BOARD_WIDEVINE_OEMCRYPTO_LEVEL
+$(error BOARD_WIDEVINE_OEMCRYPTO_LEVEL not defined!)
+endif
 
 LOCAL_WHOLE_STATIC_LIBRARIES := \
-	libwvdecryptcommon
+        libwvdecryptcommon
 
 LOCAL_SHARED_LIBRARIES := \
         libstagefright_foundation       \
@@ -14,4 +18,3 @@ LOCAL_SHARED_LIBRARIES := \
 
 LOCAL_STATIC_LIBRARIES := \
         liboemcrypto                    \
-