drivers: i2c: stm32: add target mode in RTIO drivers

Implement I2C target mode in STM32 I2C RTIO drivers. The implementation
in respectively i2c_ll_stm32_v1_rtio.c and i2c_ll_stm32_v2_rtio.c is
based on the implementation of the non-RTIO drivers, respectively
i2c_ll_stm32_v1.c and i2c_ll_stm32_v2_rtio.c.

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