modules: stm32: Rename lib Kconfig symbol

Both ST and STM32 modules where using same HAS_STLIB Kconfig
symbol.
Now that each module is createing is own lib, we need to be able
to distinguish libs.

Depends on zephyrproject-rtos/hal_stm32/pull/52

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