leds: Add support for setting brightness in a synchronous way

There are use cases when setting a LED brightness has to
have immediate effect (e.g. setting a torch LED brightness).
This patch extends LED subsystem to support such operations.
The LED subsystem internal API __led_set_brightness is changed
to led_set_brightness_async and new led_set_brightness_sync API
is added.

Signed-off-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Richard Purdie <rpurdie@rpsys.net>
Signed-off-by: Bryan Wu <cooloney@gmail.com>

diff --cc drivers/leds/led-class.c
Simple merge

diff --cc drivers/leds/led-core.c
Simple merge

diff --cc drivers/leds/leds.h
Simple merge

diff --cc drivers/leds/trigger/ledtrig-backlight.c
Simple merge

diff --cc drivers/leds/trigger/ledtrig-default-on.c
Simple merge

diff --cc drivers/leds/trigger/ledtrig-gpio.c
Simple merge

diff --cc drivers/leds/trigger/ledtrig-heartbeat.c
Simple merge

diff --cc drivers/leds/trigger/ledtrig-oneshot.c
Simple merge

diff --cc drivers/leds/trigger/ledtrig-transient.c
Simple merge

diff --cc include/linux/leds.h
Simple merge