drivers: i2c_ll_stm32_v2: add support for optional timing property

In case optional timings property has been defined in DT, let's use it
and look for a matching peripheral clock and i2c bus clock so that
timing value is used instead of using runtime algorithm.

If matching the current configuration, the value will be set directly to
the I2C_TIMINGR register through the LL API.

This property is only valid for I2C V2 peripheral, so the timing config
structure member is only added in case of CONFIG_I2C_STM32_V2. Also the
initialization of the member is done conditionnaly, only in case
it is defined in DT, otherwise timings table will be empty.

Signed-off-by: Laurent Meunier <laurent.meunier@st.com>