fbdev: Send old blank state in FB_EVENT_BLANK

fbdev: Send old blank state in FB_EVENT_BLANK

The event FB_EVENT_BLANK sends the new blank state in the event's
data field. Also send the old state. It's an additional field in the
data array; existing receivers won't notice the difference.

The backlight subsystem currently tracks blank state per display per
backlight. That is not optimal as it ties backlight code to fbdev. A
subsystem should not track internal state of another subsystem. With
both, new and old, blank state in FB_EVENT_BLANK, the backlight code
will not require its own state tracker any longer.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Link: https://lore.kernel.org/r/20250321095517.313713-4-tzimmermann@suse.de
Signed-off-by: Lee Jones <lee@kernel.org>