drivers: clock_control: stm32: don't enable RUNTIME_NMI all the time

The Clock Security System (CSS) feature signals failure of an external
oscillator by triggering an NMI. As such, when this feature is enabled,
RUNTIME_NMI must also be enabled such that the NMI handler can be modified
to point to the appropriate function.

The STM32 clock control Kconfig checks whether the CSS has been enabled in
Device Tree, and forcefully selects RUNTIME_NMI if enabled since the driver
code will require it. However, the check has been implemented improperly:
"dt_nodelabel_has_prop" was used instead of "dt_nodelabel_bool_prop", an
error similar to using DT_NODE_HAS_PROP() instead of DT_PROP() in C code.

Since the property always exists, as long as the HSE is enabled, the
RUNTIME_NMI option is always select'ed, even if not actually required.

Use the correct Kconfig function to ensure RUNTIME_NMI is select'ed only
when it is required, instead of whenever HSE is enabled regardless of CSS.

Signed-off-by: Mathieu Choplain <mathieu.choplain@st.com>