backlight: drop EARLY_EVENT_BLANK support

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