flash: update stm32 flash_f3x to support LL clock control driver

After introducing STM32Cube based clock control driver for
stm32 family, update stm32f3xx flash driver to support it.
Clean up will be done afterwards.

Change-Id: I3260bb063f714fa29adbc71d8036f20479a99b34
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>
3 files changed