ARM: dts: exynos: Add flash support to Galaxy S3 boards

The Galaxy S3 boards use an aat1290 to control the flash LED.  Add the
relevant device tree configuration to use it.

Signed-off-by: Simon Shields <simon@lineageos.org>
Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@cyberdimension.org> [rebase]
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>