hal_stm32: rename HAS_STLIB in HAS_STM32LIB

Both modules ST and STM32 use the same HAS_STLIB Kconfig symbol.
This is not coherent, so rename the one used in stm32 module
as HAS_STM32LIB

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