bootstage: Plumb in bootstage calls for basic operations

This inserts bootstage calls into tftp, usb start and bootm. We
could go further, but this is a reasonable start to illustrate
the concept.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/common/cmd_net.c b/common/cmd_net.c
index 6139188..65f32bce 100644
--- a/common/cmd_net.c
+++ b/common/cmd_net.c
@@ -43,7 +43,12 @@
 
 int do_tftpb (cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
-	return netboot_common(TFTPGET, cmdtp, argc, argv);
+	int ret;
+
+	bootstage_mark_name(BOOTSTAGE_KERNELREAD_START, "tftp_start");
+	ret = netboot_common(TFTPGET, cmdtp, argc, argv);
+	bootstage_mark_name(BOOTSTAGE_KERNELREAD_STOP, "tftp_done");
+	return ret;
 }
 
 U_BOOT_CMD(