dts: clock: stm32 configure ahb prescaler for HCLK

AHB prescaler is a value which divides the SYSCLOCK
to provide the HCLK. The HCLK supplies the core, AHB bus, memory.
On the stm32wb and stm32wl, the HCLK for CPU1 is HCLK1
with cpu1-prescaler.
By default the value is 1, else the HCLK must be correctly set.

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