arm: dts: st: Convert STM32F3 based boards to dts

Converted over all STM32F3 based boards to use device tree and removed
associated bits that now come from the device tree for STM32F3.

Boards that are now using devicetree:
* Nucleo f334r8
* STM32373C Eval

Change-Id: I081a1d83f86e417a98b6864c745354b6b32953b7
Signed-off-by: Kumar Gala <kumar.gala@linaro.org>