backlight: drop EARLY_EVENT_BLANK support

There was no users left - so drop the code to support EARLY_EVENT_BLANK.
This patch removes the support in backlight,
and drop the notifier in fbmem.

That EARLY_EVENT_BLANK is not used can be verified that no driver set any of:

    lcd_ops.early_set_power()
    lcd_ops.r_early_set_power()

Noticed while browsing backlight code for other reasons.

v2:
- Fix changelog to say "EARLY_EVENT_BLANK" (Daniel)

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: Peter Rosin <peda@axentia.se>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-fbdev@vger.kernel.org
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Acked-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190725143224.GB31803@ravnborg.org

include/linux/lcd.h

@@ -41,16 +41,6 @@ struct lcd_ops {
 	/* Get the LCD panel power status (0: full on, 1..3: controller
 	   power on, flat panel power off, 4: full off), see FB_BLANK_XXX */
 	int (*get_power)(struct lcd_device *);
-	/*
-	 * Enable or disable power to the LCD(0: on; 4: off, see FB_BLANK_XXX)
-	 * and this callback would be called proir to fb driver's callback.
-	 *
-	 * P.S. note that if early_set_power is not NULL then early fb notifier
-	 *	would be registered.
-	 */
-	int (*early_set_power)(struct lcd_device *, int power);
-	/* revert the effects of the early blank event. */
-	int (*r_early_set_power)(struct lcd_device *, int power);
 	/* Enable or disable power to the LCD (0: on; 4: off, see FB_BLANK_XXX) */
 	int (*set_power)(struct lcd_device *, int power);
 	/* Get the current contrast setting (0-max_contrast) */