gralloc: Refactor gralloc4.0 for some concerns in code review

There were some concerns raised in the intern code review process. Since
Qualcomm has merged their Gralloc4.0 changes into their codebase, the
patch created another standlane change to address the concerns within
the code review.

Bug: 141596968
Test: VtsHalGraphicsMapperV4_0TargetTest
Change-Id: Ie687557089064a6d02c7505f2024db6a23e003c8
6 files changed