drm/cma-helper: Add DRM_GEM_CMA_DRIVER_OPS to set default GEM CMA functions

The macro to DRM_GEM_CMA_DRIVER_OPS sets GEM callbacks in struct drm_driver
to their defaults for CMA. A variant of the macro is provided for drivers
that override the default .dumb_create callback. Adapt drivers to the changes.

v4:
	* remove parenthesis around dumb_create_func
	* fix grammar in commit message

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200605073247.4057-4-tzimmermann@suse.de