bootstd: Update bootmeth_alloc_file() to record images

As a first step to recording images and where they came from, update
this function to do so, since it is used by two bootmeths

Create a helper function in the bootflow system, since recorded
images are always associated with bootflows.

Signed-off-by: Simon Glass <sjg@chromium.org>

boot/bootmeth_script.c

@@ -98,7 +98,8 @@ static int script_read_bootflow_file(struct udevice *bootstd,
 	if (!bflow->subdir)
 		return log_msg_ret("prefix", -ENOMEM);
 
-	ret = bootmeth_alloc_file(bflow, 0x10000, ARCH_DMA_MINALIGN);
+	ret = bootmeth_alloc_file(bflow, 0x10000, ARCH_DMA_MINALIGN,
+				  (enum bootflow_img_t)IH_TYPE_SCRIPT);
 	if (ret)
 		return log_msg_ret("read", ret);