drm/panel/raspberrypi-touchscreen: Initialise the bridge in prepare

The panel has a prepare call which is before video starts, and an
enable call which is after.
The Toshiba bridge should be configured before video, so move
the relevant power and initialisation calls to prepare.

Fixes: 2f733d61 ("drm/panel: Add support for the Raspberry Pi 7" Touchscreen.")
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220415162513.42190-3-stefan.wahren@i2se.com

drivers/gpu/drm/panel/panel-raspberrypi-touchscreen.c

@@ -265,7 +265,7 @@ static int rpi_touchscreen_noop(struct drm_panel *panel)
 	return 0;
 }
 
-static int rpi_touchscreen_enable(struct drm_panel *panel)
+static int rpi_touchscreen_prepare(struct drm_panel *panel)
 {
 	struct rpi_touchscreen *ts = panel_to_ts(panel);
 	int i;
@@ -295,6 +295,13 @@ static int rpi_touchscreen_enable(struct drm_panel *panel)
 	rpi_touchscreen_write(ts, DSI_STARTDSI, 0x01);
 	msleep(100);
 
+	return 0;
+}
+
+static int rpi_touchscreen_enable(struct drm_panel *panel)
+{
+	struct rpi_touchscreen *ts = panel_to_ts(panel);
+
 	/* Turn on the backlight. */
 	rpi_touchscreen_i2c_write(ts, REG_PWM, 255);
 
@@ -349,7 +356,7 @@ static int rpi_touchscreen_get_modes(struct drm_panel *panel,
 static const struct drm_panel_funcs rpi_touchscreen_funcs = {
 	.disable = rpi_touchscreen_disable,
 	.unprepare = rpi_touchscreen_noop,
-	.prepare = rpi_touchscreen_noop,
+	.prepare = rpi_touchscreen_prepare,
 	.enable = rpi_touchscreen_enable,
 	.get_modes = rpi_touchscreen_get_modes,
 };