drivers/video/backlight/backlight.c: remove backlight sysfs uevent

drivers/video/backlight/backlight.c: remove backlight sysfs uevent

Most mobile phones have Ambient Light Sensors and it changes brightness
according to the lux.  It means it changes backlight brightness frequently
by just writing sysfs node, so it generates uevent.

Usually there's no user to use this backlight changes.  But it forks udev
worker threads and it takes about 5ms.  The main problem is that it hurts
other process activities.  so remove it.

Kay said
"Uevents are for the major, low-frequent, global device state-changes,
 not for carrying-out any sort of measurement data. Subsystems which
 need that should use other facilities like poll()-able sysfs file or
 any other subscription-based, client-tracking interface which does not
 cause overhead if it isn't used. Uevents are not the right thing to
 use here, and upstream udev should not paper-over broken kernel
 subsystems."

Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Henrique de Moraes Holschuh <hmh@hmh.eng.br>
Cc: Matthew Garrett <mjg59@srcf.ucam.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Cc: Henrique de Moraes Holschuh <ibm-acpi@hmh.eng.br>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>