dt-bindings: arm: stm32: Add missing STM32 boards

This commit documents missing STM32 boards:

-STM32MCU: F429 disco/eval, F469-disco, F746 disco/eval, F769 disco,
H743 disco/eval.

-STM32MPU: MP157 dk1/dk2/ed1/ev1.

Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>
Signed-off-by: Rob Herring <robh@kernel.org>