DT: leds: Add flash LED devices related properties

Addition of a LED Flash class extension entails the need for flash LED
specific device tree properties. The properties being added are:
max-microamp, flash-max-microamp, flash-timeout-microsec.

(cooloney@gmail.com: remove white spaces)

Signed-off-by: Pavel Machek <pavel@ucw.cz>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Acked-by: Jacek Anaszewski <j.anaszewski@samsung.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bryan Wu <cooloney@gmail.com>