leds: aat1290: Move driver to flash subdirectory

We created a subdirectory for LED drivers that depend on
CONFIG_LEDS_CLASS_FLASH, and this driver does so let's
move it there.

Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Pavel Machek <pavel@ucw.cz>