gralloc1: Fix for buffer mapping and metadata access

- Don't mmap in the allocator process as it is unnecessary
- Fix MetaData access through getMetaData API
- Eventually we need to remove the MapBuffer in RetainBuffer to
fix 35955598.

Acked-by: Prabhanjan Kandula <pkandula@codeaurora.org>
CRs-Fixed: 2025987
Change-Id: I3d3a0edcf6ec93e827582010f6936361cb3790dd
2 files changed