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
diff --git a/drivers/gpu/drm/tinydrm/ili9225.c b/drivers/gpu/drm/tinydrm/ili9225.c
index 3b766a2..e8f1b3a 100644
--- a/drivers/gpu/drm/tinydrm/ili9225.c
+++ b/drivers/gpu/drm/tinydrm/ili9225.c
@@ -20,6 +20,7 @@
 #include <linux/spi/spi.h>
 #include <video/mipi_display.h>
 
+#include <drm/drm_fb_helper.h>
 #include <drm/drm_gem_framebuffer_helper.h>
 #include <drm/tinydrm/mipi-dbi.h>
 #include <drm/tinydrm/tinydrm-helpers.h>
@@ -381,7 +382,7 @@ static struct drm_driver ili9225_driver = {
 				  DRIVER_ATOMIC,
 	.fops			= &ili9225_fops,
 	TINYDRM_GEM_DRIVER_OPS,
-	.lastclose		= tinydrm_lastclose,
+	.lastclose		= drm_fb_helper_lastclose,
 	.name			= "ili9225",
 	.desc			= "Ilitek ILI9225",
 	.date			= "20171106",