exynos4: Set libgralloc_ump and SecHdmi tags to optional

When LOCAL_MODULE_TAGS was set to eng this broke eng builds
due to the lack of source for libsamsungion. Set the tag to
optional so it is not built for an eng build.

Change-Id: I770c991dc16ccce9905501619e015567110de577
Merge remote-tracking branch 'upstream/jellybean' into jellybean