refactor(st): configure baudrate for UART programmer

Add the possibility to configure the UART baudrate; reused the
console configuration, defined in STM32MP_UART_BAUDRATE.

The default value remains 115200.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Change-Id: Ifcf2b36e8ac929265405bc88e824ee78be3b5bbb
1 file changed