drm_hwcomposer: Support Nvidia gralloc

When using an Nvidia gralloc implementation, ask Nvidia gralloc to import the
buffer_handle_t to the hwcomposer's drm device.

Arguably, the code to perform the import would more naturally belong to
drm_hwcomposer than Nvidia gralloc.  But letting Nvidia gralloc do it has two
advantages.  First, drm_hwcomposer doesn't need to include vendor headers or
link against vendor libraries.  This means that it's easy to support both
drm_gralloc and Nvidia gralloc from the same default build of drm_hwcomposer.
Second, Nvidia gralloc will take care of properly setting up any vendor
specific metadata (such as tiling parameters) of the imported GEM handle.

Change-Id: I0f77fb301e7e0bff2a8cd7befeae4bc4892220ad
Reviewed-on: https://chrome-internal-review.googlesource.com/195115
Reviewed-by: Stéphane Marchesin <marcheu@google.com>
Commit-Queue: Stéphane Marchesin <marcheu@google.com>
Tested-by: Stéphane Marchesin <marcheu@google.com>
diff --git a/drm_hwcomposer.h b/drm_hwcomposer.h
index a83acab..35b3aa9 100644
--- a/drm_hwcomposer.h
+++ b/drm_hwcomposer.h
@@ -16,6 +16,10 @@
 
 struct hwc_import_context;
 
+enum {
+       GRALLOC_MODULE_PERFORM_DRM_IMPORT = 0xffeeff00
+};
+
 struct hwc_drm_bo {
 	uint32_t width;
 	uint32_t height;