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>

include/configs/stm32h750-art-pi.h

@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright (C) 2021, STMicroelectronics - All Rights Reserved
+ * Author(s): Dillon Min <dillon.minfei@gmail.com>
+ */
+
+#ifndef __CONFIG_H
+#define __CONFIG_H
+
+#include <config.h>
+#include <linux/sizes.h>
+
+/* For booting Linux, use the first 16MB of memory */
+#define CONFIG_SYS_BOOTMAPSZ		(SZ_16M + SZ_8M)
+
+#define CONFIG_SYS_FLASH_BASE		0x90000000
+#define CONFIG_SYS_INIT_SP_ADDR		0x24040000
+
+/*
+ * Configuration of the external SDRAM memory
+ */
+#define CONFIG_SYS_LOAD_ADDR		0xC1800000
+#define CONFIG_LOADADDR			0xC1800000
+
+#define CONFIG_SYS_HZ_CLOCK		1000000
+
+#define CONFIG_CMDLINE_TAG
+#define CONFIG_SETUP_MEMORY_TAGS
+#define CONFIG_INITRD_TAG
+#define CONFIG_REVISION_TAG
+
+#define CONFIG_SYS_MAXARGS		16
+#define CONFIG_SYS_MALLOC_LEN		(1 * 1024 * 1024)
+
+#define BOOT_TARGET_DEVICES(func) \
+	func(MMC, mmc, 0)
+
+#include <config_distro_bootcmd.h>
+#define CONFIG_EXTRA_ENV_SETTINGS				\
+			"kernel_addr_r=0xC0008000\0"		\
+			"fdtfile=stm32h750i-art-pi.dtb\0"	\
+			"fdt_addr_r=0xC0408000\0"		\
+			"scriptaddr=0xC0418000\0"		\
+			"pxefile_addr_r=0xC0428000\0" \
+			"ramdisk_addr_r=0xC0438000\0"		\
+			BOOTENV
+
+#endif /* __CONFIG_H */