dts: arm: stm32: update Vref nodes with non-standard resolution

After updating the "st,stm32-vref" binding with a new property containing
the calibration data resolution ("vrefint-cal-resolution"), update the
corresponding nodes in SoC DTSI files with the proper value.

Note that the property is not set on SoCs with resolution of 12, as it is
the default value specified for the property in the binding.

Signed-off-by: Mathieu Choplain <mathieu.choplain@st.com>