drm: Move simple_display_pipe prepare_fb helper into gem fb helpers

There's nothing tinydrm specific to this, and there's a few more
copies of the same in various other drivers.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Gustavo Padovan <gustavo@padovan.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: David Airlie <airlied@linux.ie>
Cc: David Lechner <david@lechnology.com>
Cc: "Noralf Trønnes" <noralf@tronnes.org>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Neil Armstrong <narmstrong@baylibre.com>
Cc: Daniel Stone <daniels@collabora.com>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Ben Widawsky <ben@bwidawsk.net>
Cc: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
Reviewed-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@epam.com>
Acked-by: David Lechner <david@lechnology.com>
Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180405154449.23038-3-daniel.vetter@ffwll.ch

drivers/gpu/drm/tinydrm/mi0283qt.c

@@ -19,6 +19,7 @@
 
 #include <drm/drm_fb_helper.h>
 #include <drm/drm_modeset_helper.h>
+#include <drm/drm_gem_framebuffer_helper.h>
 #include <drm/tinydrm/mipi-dbi.h>
 #include <drm/tinydrm/tinydrm-helpers.h>
 #include <video/mipi_display.h>
@@ -134,7 +135,7 @@ static const struct drm_simple_display_pipe_funcs mi0283qt_pipe_funcs = {
 	.enable = mi0283qt_enable,
 	.disable = mipi_dbi_pipe_disable,
 	.update = tinydrm_display_pipe_update,
-	.prepare_fb = tinydrm_display_pipe_prepare_fb,
+	.prepare_fb = drm_gem_fb_simple_display_pipe_prepare_fb,
 };
 
 static const struct drm_display_mode mi0283qt_mode = {