arm: dts: st: Convert STM32F4 based boards to dts

Converted over all STM32F4 based boards to use device tree and removed
associated bits that now come from the device tree for STM32F4.

Boards that are now using devicetree:
* 96b_carbon
* nucleo f401re
* nucleo f411re

Change-Id: Ibe197ca0a3f5ad78d594485a578d986403cc824a
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>