ARM: stm32: add new STM32F769 MCU

Add new st,stm32f769 compatible machine name for STM32F769 MCU and update
documentation.

Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>

arch/arm/mach-stm32/board-dt.c

@@ -12,6 +12,7 @@ static const char *const stm32_compat[] __initconst = {
 	"st,stm32f429",
 	"st,stm32f469",
 	"st,stm32f746",
+	"st,stm32f769",
 	"st,stm32h743",
 	NULL
 };