boards: arduino_giga: allow memory mapping external QSPI flash

Author: facchinm

boards/arduino/giga_r1/arduino_giga_r1_stm32h747xx_m7.dts

@@ -33,6 +33,14 @@
 		zephyr,memory-attr = <( DT_MEM_ARM(ATTR_MPU_RAM) )>;
 	};
 
+	ext_memory: memory@90000000 {
+		compatible = "zephyr,memory-region";
+		reg = <0x90000000 DT_SIZE_M(16)>; /* max addressable area */
+		zephyr,memory-region = "EXTMEM";
+		/* The ATTR_MPU_EXTMEM attribut causing a MPU FAULT */
+		zephyr,memory-attr = <( DT_MEM_ARM(ATTR_MPU_IO) )>;
+	};
+
 	aliases {
 		led0 = &red_led;
 		led1 = &green_led;