RT #112561. Enable FDT booting on STM32F4 SOMs

Also fix a bug in arch_lmb_reserve() ARM procedure, which reveals
itself (as 'device tree allocation error') when we have stack not
in external RAM, and try booting with FDT.
Signed-off-by: Yuri Tikhonov <yur@emcraft.com>

include/configs/stm-som.h

@@ -469,4 +469,17 @@
 #define CONFIG_SETUP_MEMORY_TAGS
 #define CONFIG_CMDLINE_TAG
 
+/*
+ * Enable support for booting with FDT
+ */
+#define CONFIG_OF_LIBFDT
+
+/*
+ * The early kernel mapping on ARM currently only maps from the base of DRAM
+ * to the end of the kernel image.  The kernel is loaded at DRAM base + 0x8000.
+ * The early kernel pagetable uses DRAM base + 0x4000 to DRAM base + 0x8000,
+ * so that leaves DRAM base to DRAM base + 0x4000 available.
+ */
+#define CONFIG_SYS_BOOTMAPSZ		0x4000
+
 #endif /* __CONFIG_H */

lib_arm/bootm.c

@@ -87,8 +87,15 @@ void arch_lmb_reserve(struct lmb *lmb)
 
 	/* adjust sp by 1K to be safe */
 	sp -= 1024;
-	lmb_reserve(lmb, sp,
-		    gd->bd->bi_dram[0].start + gd->bd->bi_dram[0].size - sp);
+
+	/*
+	 * Skip reservation if our stack is not in external RAM
+	 */
+	if (sp >= gd->bd->bi_dram[0].start &&
+	    sp <  gd->bd->bi_dram[0].start + gd->bd->bi_dram[0].size) {
+		lmb_reserve(lmb, sp, gd->bd->bi_dram[0].start +
+			    gd->bd->bi_dram[0].size - sp);
+	}
 }
 
 static void announce_and_cleanup(void)