drm/tinydrm: Use drm_fb_cma_fbdev_init_with_funcs/fini()

Use drm_fb_cma_fbdev_init_with_funcs() and drm_fb_cma_fbdev_fini() which
relies on the fact that drm_device holds a pointer to the drm_fb_helper
structure. This means that the driver doesn't have to keep track of that.
Also use the drm_fb_helper functions directly.
Remove todo entry.

Cc: David Lechner <david@lechnology.com>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: David Lechner <david@lechnology.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Tested-by: David Lechner <david@lechnolgy.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171208193743.34450-11-noralf@tronnes.org

drivers/gpu/drm/tinydrm/mi0283qt.c

@@ -9,6 +9,7 @@
  * (at your option) any later version.
  */
 
+#include <drm/drm_fb_helper.h>
 #include <drm/drm_modeset_helper.h>
 #include <drm/tinydrm/ili9341.h>
 #include <drm/tinydrm/mipi-dbi.h>
@@ -140,7 +141,7 @@ static struct drm_driver mi0283qt_driver = {
 				  DRIVER_ATOMIC,
 	.fops			= &mi0283qt_fops,
 	TINYDRM_GEM_DRIVER_OPS,
-	.lastclose		= tinydrm_lastclose,
+	.lastclose		= drm_fb_helper_lastclose,
 	.debugfs_init		= mipi_dbi_debugfs_init,
 	.name			= "mi0283qt",
 	.desc			= "Multi-Inno MI0283QT",