hw/char/stm32l4x5_usart: Enable serial read and write

Implement the ability to read and write characters to the
usart using the serial port.

The character transmission is based on the
cmsdk-apb-uart implementation.

Signed-off-by: Arnaud Minier <arnaud.minier@telecom-paris.fr>
Signed-off-by: Inès Varhol <ines.varhol@telecom-paris.fr>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20240329174402.60382-3-arnaud.minier@telecom-paris.fr
[PMM: fixed a few checkpatch nits]
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
3 files changed