include: zephyr: dt-bindings: clock: factorize STM32_* clock source macros

Factorize definitions of the macros used to describe in the STM32
boards device tree the RCC register dedicated to clock source selection
configuration, instead of replicating the macros per SoC header file.
For that purpose, use DT cell bit fields that matches all SoCs.

This change also factorizes STM32_MCO_CFGR_* macros that use the same
packing layout for defining selection of the MCO clocks and for MCO
pre-scaling factor on SoCs that support the feature.

By the way, reorder argument description in macro inline description
comment in a standard way (first argument first).

Signed-off-by: Etienne Carriere <etienne.carriere@st.com>