arm: dts: mt6323: move node mt6323 leds to mt6323.dtsi

Since those LEDs are parts of PMIC MT6323, it is reasonable to merge
those LEDs node definition back into mt6323.dtsi. This way can improve
the reusability of those nodes among different boards with the same PMIC.

And LED is very much board specific and thus the mt6323.dtsi only includes
the parent node here and leave these child nodes in the board specific
dts file.

Signed-off-by: Sean Wang <sean.wang@mediatek.com>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Rob Herring <robh+dt@kernel.org>
Signed-off-by: Matthias Brugger <matthias.bgg@gmail.com>