graphics: Update RAW16 format comments

RAW16 format could be used together with depth dataspace.
The buffer contents in this case will be phase detection
statistics data.

Bug: 36015382
Test: testPDStats
Change-Id: Ied1c179193abef62a87fcec6f0906528ed58ea2b
(cherry picked from commit 23699d63143fd9d47f8584c6627e5c38838b333f)
diff --git a/graphics/common/1.0/types.hal b/graphics/common/1.0/types.hal
index 979e4c4..8aa0779 100644
--- a/graphics/common/1.0/types.hal
+++ b/graphics/common/1.0/types.hal
@@ -181,9 +181,17 @@
      *    - GRALLOC_USAGE_SW_*
      *    - GRALLOC_USAGE_RENDERSCRIPT
      *
-     * When used with ANativeWindow, the dataSpace should be
-     * HAL_DATASPACE_ARBITRARY, as raw image sensor buffers require substantial
-     * extra metadata to define.
+     * When used with ANativeWindow, the mapping of the dataSpace field to
+     * buffer contents for RAW16 is as follows:
+     *
+     *  dataSpace value               | Buffer contents
+     * -------------------------------+-----------------------------------------
+     *  HAL_DATASPACE_ARBITRARY       | Raw image sensor data, layout is as
+     *                                | defined above.
+     *  HAL_DATASPACE_DEPTH           | Unprocessed implementation-dependent raw
+     *                                | depth measurements, opaque with 16 bit
+     *                                | samples.
+     *  Other                         | Unsupported
      */
     RAW16 = 0x20,