refactor(st): configure UART baudrate

Add the possibility to configure console UART baudrate, it can be passed
as a command line parameter with STM32MP_UART_BAUDRATE. The default value
remains 115200.

Signed-off-by: Yann Gautier <yann.gautier@foss.st.com>
Change-Id: I000df70c10b2b4dac1449556596f9820c36cf243
diff --git a/docs/plat/stm32mp1.rst b/docs/plat/stm32mp1.rst
index 8b6f979..cefc21f 100644
--- a/docs/plat/stm32mp1.rst
+++ b/docs/plat/stm32mp1.rst
@@ -127,6 +127,8 @@
   | Default: stm32mp157c-ev1.dtb
 - | ``STM32MP_EARLY_CONSOLE``: to enable early traces before clock driver is setup.
   | Default: 0 (disabled)
+- | ``STM32MP_UART_BAUDRATE``: to select UART baud rate.
+  | Default: 115200
 - | ``STM32_TF_VERSION``: to manage BL2 monotonic counter.
   | Default: 0