soc: stm32wba: hci_if: Implement HW_RNG_EnableClock API

STM32WBA controller uses a PKA driver to perform cyphering operations
on keys. Since PKA hardware block requires RNG clock to be enabled, a
synchronization with zephyr RNG driver is needed.

Use RNG enable status to check if RNG could be switched off or needs to
be switched on.
Similarly in entropy driver, don't cut RNG clock if PKA is enabled.

Signed-off-by: Erwan Gouriou <erwan.gouriou@st.com>