serial: stm32x7: Convert CONFIG_STM32X7_SERIAL to Kconfig

Add CONFIG_STM32X7_SERIAL as a Kconfig option.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
Reviewed-by: Vikas Manocha <vikas.manocha@st.com>
4 files changed