board: Add rt-thread art-pi board support

All these files are add for support rt-thread art-pi board
- add board/st/stm32h750-art-pi, defconfig, header support for u-boot

for more information about art-pi, please goto:
https://art-pi.gitee.io/website/

Signed-off-by: dillon min <dillon.minfei@gmail.com>
Reviewed-by: Patrice Chotard <patrice.chotard@foss.st.com>
diff --git a/arch/arm/mach-stm32/stm32h7/Kconfig b/arch/arm/mach-stm32/stm32h7/Kconfig
index 55e6217..70233a4 100644
--- a/arch/arm/mach-stm32/stm32h7/Kconfig
+++ b/arch/arm/mach-stm32/stm32h7/Kconfig
@@ -6,7 +6,11 @@
 config TARGET_STM32H743_EVAL
 	bool "STM32H743 Evaluation board"
 
+config TARGET_STM32H750_ART_PI
+	bool "STM32H750 ART Pi board"
+
 source "board/st/stm32h743-eval/Kconfig"
 source "board/st/stm32h743-disco/Kconfig"
+source "board/st/stm32h750-art-pi/Kconfig"
 
 endif