gralloc: add get and set BufferMetadata support

Add get and set functions that allow buffer metadata to be set
on the buffer.

This patch has been reviewed by vendors on AOSP. It is a combination of the
following patches. They have been squashed (and updated) to make them easier to
review. Two of the patches are proposals by ARM that have been incorporated into
this patch.

https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1107574
https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1109946
https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1124857
https://android-review.googlesource.com/c/platform/hardware/interfaces/+/1126861

Bug: 141632767, 141631993
Test: VtsHalGraphicsMapperV4_0TargetTest

Change-Id: I0e79d73a7687f2f5b51828a7454888e6d8ff9460