drivers: stm32: do not enable the HSI48 locally

The HSI48 is enabled by clock control driver.
It is no more done by each driver that requires this clock
However when using rng or sdmmc or bluetooth/ipm or usb,
the HSI48 clock must be present in the DTS.
Add a warning for this particular check but keep the deprecated
HSI48 clock enable : keeping for legacy but to remove later.

Signed-off-by: Francois Ramu <francois.ramu@st.com>