VR: Add commands to pass buffer metadata via the VR HWC HAL

Without gralloc1 support, need to pass buffer metadata to allow buffers
to be imported and used as graphic buffers in the VR composition
pipeline.

Bug: 36481301
Test: Compiled and ran on device, started VR and ensured SurfaceFlinger
output is visible.

Change-Id: I61b146a52cfbd0d535c202319c88a90753973471