Remove the field fb_blank from struct backlight_properties and remove
all code that still sets or reads it. Backlight blank status is now
tracked exclusively in struct backlight_properties.state.

The core backlight code keeps the fb_blank and state fields in sync,
but doesn't do anything else with fb_blank. Several drivers initialize
fb_blank to FB_BLANK_UNBLANK to enable the backlight. This is already
the default for the state field. So we can delete the fb_blank code
from core and drivers and rely on the state field.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Flavio Suligoi <f.suligoi@asem.it>
Cc: Nicolas Ferre <nicolas.ferre@microchip.com>
Cc: Alexandre Belloni <alexandre.belloni@bootlin.com>
Cc: Claudiu Beznea <claudiu.beznea@tuxon.dev>
Tested-by: Flavio Suligoi <f.suligoi@asem.it>
Reviewed-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Dan Carpenter <dan.carpenter@linaro.org>
Link: https://lore.kernel.org/r/20240319093915.31778-7-tzimmermann@suse.deSigned-off-by: Lee Jones <lee@kernel.org>