drm/mipi_dbi: Use drmm_add_final_kfree in all drivers

They all share mipi_dbi_release so we need to switch them all
together. With this we can drop the final kfree from the release
function.

Aside, I think we could perhaps have a tiny additional helper for
these mipi_dbi drivers, the first few lines around devm_drm_dev_init
are all the same (except for the drm_driver pointer).

Acked-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Tested-by: Noralf Trønnes <noralf@tronnes.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Eric Anholt <eric@anholt.net>
Cc: David Lechner <david@lechnology.com>
Cc: Kamlesh Gurudasani <kamlesh.gurudasani@gmail.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200323144950.3018436-6-daniel.vetter@ffwll.ch
diff --git a/drivers/gpu/drm/tiny/st7586.c b/drivers/gpu/drm/tiny/st7586.c
index 9ef559d..427c256 100644
--- a/drivers/gpu/drm/tiny/st7586.c
+++ b/drivers/gpu/drm/tiny/st7586.c
@@ -21,6 +21,7 @@
 #include <drm/drm_format_helper.h>
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_gem_framebuffer_helper.h>
+#include <drm/drm_managed.h>
 #include <drm/drm_mipi_dbi.h>
 #include <drm/drm_rect.h>
 
@@ -328,6 +329,7 @@ static int st7586_probe(struct spi_device *spi)
 		kfree(dbidev);
 		return ret;
 	}
+	drmm_add_final_kfree(drm, dbidev);
 
 	drm_mode_config_init(drm);