New bindings and driver have been created for STM32F42xxx series parts.
This patch integrates these changes.

Note: Earlier device tree blobs (those without st,stm32f42xxx
      compatibles for the rcc) could still be used to boot basic
      systems. Such systems rely on the bootloader to configure the
      clock gates for vital periperhals.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Reviewed-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Signed-off-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>