drivers/mtd: Implement MTDIOC_ERASESTATE for MTD drivers

Signed-off-by: Gustavo Henrique Nihei <gustavo.nihei@espressif.com>

drivers/mtd/filemtd.c

@@ -449,6 +449,15 @@ static int filemtd_ioctl(FAR struct mtd_dev_s *dev, int cmd,
         }
         break;
 
+      case MTDIOC_ERASESTATE:
+        {
+          FAR uint8_t *result = (FAR uint8_t *)arg;
+          *result = CONFIG_FILEMTD_ERASESTATE;
+
+          ret = OK;
+        }
+        break;
+
       default:
         ret = -ENOTTY; /* Bad command */
         break;