drm/tinydrm: Add helper functions

Add common functionality needed by many tinydrm drivers.

Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Thierry Reding <treding@nvidia.com>

Documentation/gpu/tinydrm.rst

@@ -19,3 +19,12 @@ Core functionality
 
 .. kernel-doc:: drivers/gpu/drm/tinydrm/core/tinydrm-pipe.c
    :export:
+
+Additional helpers
+==================
+
+.. kernel-doc:: include/drm/tinydrm/tinydrm-helpers.h
+   :internal:
+
+.. kernel-doc:: drivers/gpu/drm/tinydrm/core/tinydrm-helpers.c
+   :export: