gl-renderer: support format and modifier queries

EGL_EXT_image_dma_buf_import_modifiers allows querying the formats
and modifiers supported by the platform. expose these to the compositor.

v2:
 - change calloc args (Daniel Stone)
 - check for modifier support before querying formats (Daniel Stone)

Signed-off-by: Varad Gautam <varad.gautam@collabora.com>
Reviewed-by: Daniel Stone <daniels@collabora.com>
diff --git a/libweston/compositor.h b/libweston/compositor.h
index 6070c77..50f7420 100644
--- a/libweston/compositor.h
+++ b/libweston/compositor.h
@@ -747,6 +747,13 @@
 	/** See weston_compositor_import_dmabuf() */
 	bool (*import_dmabuf)(struct weston_compositor *ec,
 			      struct linux_dmabuf_buffer *buffer);
+
+	bool (*query_dmabuf_formats)(struct weston_compositor *ec,
+				int **formats, int *num_formats);
+
+	bool (*query_dmabuf_modifiers)(struct weston_compositor *ec,
+				int format, uint64_t **modifiers,
+				int *num_modifiers);
 };
 
 enum weston_capability {