board: stm32f429-disco: switch to DM STM32 serial driver

Remove serial_stm32.c driver and uart init from board file,
use available DM serial_stm32x7.c driver compatible for
STM32F4/F7 and H7 SoCs.

The serial_stm32x7.c driver will be renamed later with a more
generic name as it's shared with all STM32 Socs.

Signed-off-by: Patrice Chotard <patrice.chotard@st.com>
5 files changed