driver: clock control stm32: align f4 factor names on l4

This commits align CONFIG_ factor names between stm32f4 and stm32l4
series to enable code factorization such as use of Q_DIVISOR.
Though, it does not concatenate kconfig sections as we might use
a bit of time to see what is needed in this regard

Change-Id: Ia603406d53949abf5675b801a5448397d5ab8462
Signed-off-by: Erwan Gouriou <erwan.gouriou@linaro.org>