stm32mp1: add runtime information in environment

Set board name with the first dts compatible found in DT
code under CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG

The result with DEVICE_TREE=stm32mp157c-ev1 is:
    STM32MP> env print
    	board=stm32mp1
    	board_name=stm32mp157c-ev1
Signed-off-by: NPatrick Delaunay <patrick.delaunay@st.com>

arch/arm/Kconfig

@@ -1403,6 +1403,7 @@ config ARCH_STM32MP
 	select SYSRESET
 	select SYS_THUMB_BUILD
 	imply CMD_DM
+	imply ENV_VARS_UBOOT_RUNTIME_CONFIG
 	help
 	  Support for STM32MP SoC family developed by STMicroelectronics,
 	  MPUs based on ARM cortex A core

board/st/stm32mp1/stm32mp1.c

@@ -220,11 +220,6 @@ int board_usb_cleanup(int index, enum usb_init_type init)
 	return 0;
 }
 
-int board_late_init(void)
-{
-	return 0;
-}
-
 /* board dependent setup after realloc */
 int board_init(void)
 {
@@ -236,3 +231,22 @@ int board_init(void)
 
 	return 0;
 }
+
+int board_late_init(void)
+{
+#ifdef CONFIG_ENV_VARS_UBOOT_RUNTIME_CONFIG
+	const void *fdt_compat;
+	int fdt_compat_len;
+
+	fdt_compat = fdt_getprop(gd->fdt_blob, 0, "compatible",
+				 &fdt_compat_len);
+	if (fdt_compat && fdt_compat_len) {
+		if (strncmp(fdt_compat, "st,", 3) != 0)
+			env_set("board_name", fdt_compat);
+		else
+			env_set("board_name", fdt_compat + 3);
+	}
+#endif
+
+	return 0;
+}