drm/cma: Introduce drm_gem_cma_dumb_create_internal()

This function is similar to drm_gem_cma_dumb_create() but targetted at
kernel internal users so that they can override the pitch and size
requirements of the dumb buffer.

It is important to make this difference because the IOCTL says that the
pitch and size fields are to be considered outputs and therefore should
not be used in computations of the framebuffer size. Internal users may
still want to use this code to avoid duplication and at the same time
pass on additional, driver-specific restrictions on the pitch and size.

While at it, convert the R-Car DU driver, the single user that overrides
the pitch, to use the new internal helper.

Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Thierry Reding <treding@nvidia.com>

include/drm/drm_gem_cma_helper.h

@@ -29,6 +29,11 @@ to_drm_gem_cma_obj(struct drm_gem_object *gem_obj)
 /* free GEM object */
 void drm_gem_cma_free_object(struct drm_gem_object *gem_obj);
 
+/* create memory region for DRM framebuffer */
+int drm_gem_cma_dumb_create_internal(struct drm_file *file_priv,
+				     struct drm_device *drm,
+				     struct drm_mode_create_dumb *args);
+
 /* create memory region for DRM framebuffer */
 int drm_gem_cma_dumb_create(struct drm_file *file_priv,
 			    struct drm_device *drm,