Add the voicemail provider to the core packages.

Change-Id: I6a9f14a1129afffa0f80fb33977a98654ea61ccf
diff --git a/target/product/core.mk b/target/product/core.mk
index e9c8cbc..bdb1c71 100644
--- a/target/product/core.mk
+++ b/target/product/core.mk
@@ -75,6 +75,7 @@
     ApplicationsProvider \
     BackupRestoreConfirmation \
     ContactsProvider \
+    VoicemailProvider \
     DownloadProvider \
     DownloadProviderUi \
     MediaProvider \