ARM: dts: stm32f429: Adopt STM32 RNG driver

New bindings and driver have been created for STM32 series parts. This
patch integrates this changes.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Maxime Coquelin <mcoquelin.stm32@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>