drm/sun4i: abstract a engine type

As we are going to add support for the Allwinner DE2 engine in sun4i-drm
driver, we will finally have two types of display engines -- the DE1
backend and the DE2 mixer. They both do some display blending and feed
graphics data to TCON, and is part of the "Display Engine" called by
Allwinner, so I choose to call them both "engine" here.

Abstract the engine type to a new struct with an ops struct, which contains
functions that should be called outside the engine-specified code (in
TCON, CRTC or TV Encoder code).

In order to preserve bisectability, we also switch the backend and layer
code in its own module.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Reviewed-by: Chen-Yu Tsai <wens@csie.org>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>

drivers/gpu/drm/sun4i/sun4i_crtc.c

@@ -25,10 +25,9 @@
 
 #include <video/videomode.h>
 
-#include "sun4i_backend.h"
 #include "sun4i_crtc.h"
 #include "sun4i_drv.h"
-#include "sun4i_layer.h"
+#include "sunxi_engine.h"
 #include "sun4i_tcon.h"
 
 static void sun4i_crtc_atomic_begin(struct drm_crtc *crtc,
@@ -56,7 +55,7 @@ static void sun4i_crtc_atomic_flush(struct drm_crtc *crtc,
 
 	DRM_DEBUG_DRIVER("Committing plane changes\n");
 
-	sun4i_backend_commit(scrtc->backend);
+	sunxi_engine_commit(scrtc->engine);
 
 	if (event) {
 		crtc->state->event = NULL;
@@ -135,7 +134,7 @@ static const struct drm_crtc_funcs sun4i_crtc_funcs = {
 };
 
 struct sun4i_crtc *sun4i_crtc_init(struct drm_device *drm,
-				   struct sun4i_backend *backend,
+				   struct sunxi_engine *engine,
 				   struct sun4i_tcon *tcon)
 {
 	struct sun4i_crtc *scrtc;
@@ -146,11 +145,11 @@ struct sun4i_crtc *sun4i_crtc_init(struct drm_device *drm,
 	scrtc = devm_kzalloc(drm->dev, sizeof(*scrtc), GFP_KERNEL);
 	if (!scrtc)
 		return ERR_PTR(-ENOMEM);
-	scrtc->backend = backend;
+	scrtc->engine = engine;
 	scrtc->tcon = tcon;
 
 	/* Create our layers */
-	planes = sun4i_layers_init(drm, scrtc);
+	planes = sunxi_engine_layers_init(drm, engine);
 	if (IS_ERR(planes)) {
 		dev_err(drm->dev, "Couldn't create the planes\n");
 		return NULL;