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_bootm.c b/common/cmd_bootm.c
index fd9f3e9..d88f6c0 100644
--- a/common/cmd_bootm.c
+++ b/common/cmd_bootm.c
@@ -199,6 +199,8 @@
 
 	bootm_start_lmb();
 
+	bootstage_mark_name(BOOTSTAGE_ID_BOOTM_START, "bootm_start");
+
 	/* get kernel image header, start address and length */
 	os_hdr = boot_get_kernel(cmdtp, flag, argc, argv,
 			&images, &images.os.image_start, &images.os.image_len);