i2c: stm32: add support for the st,stm32mp13 SOC

The stm32mp13 soc differs from the stm32mp15 in terms of
clear register offset for controlling the FMP (Fast Mode Plus).

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>