boot: Update extlinux pxe_getfile_func() to include type

Add a file-type parameter to this function and update all users. Add a
proper comment to the function which we are here.

This will allow tracking of the file types loaded by the extlinux
bootmeth.

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

boot/bootmeth_extlinux.c

@@ -68,7 +68,8 @@ static int extlinux_get_state_desc(struct udevice *dev, char *buf, int maxsize)
 }
 
 static int extlinux_getfile(struct pxe_context *ctx, const char *file_path,
-			    char *file_addr, ulong *sizep)
+			    char *file_addr, enum bootflow_img_t type,
+			    ulong *sizep)
 {
 	struct extlinux_info *info = ctx->userdata;
 	ulong addr;
@@ -79,7 +80,7 @@ static int extlinux_getfile(struct pxe_context *ctx, const char *file_path,
 	/* Allow up to 1GB */
 	*sizep = 1 << 30;
 	ret = bootmeth_read_file(info->dev, info->bflow, file_path, addr,
-				 (enum bootflow_img_t)IH_TYPE_INVALID, sizep);
+				 type, sizep);
 	if (ret)
 		return log_msg_ret("read", ret);