x86: coreboot: Sync up timestamp codes

Add new timestamp codes that are present in coreboot, so that we can decode
these in U-Boot.

At present TS_U_BOOT_START_KERNEL is used twice. It should only be used
just before jumping to Linux, so update the other call site to use
TS_START_KERNEL.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/x86/lib/bootm.c b/arch/x86/lib/bootm.c
index aa5f0bf..733dd71 100644
--- a/arch/x86/lib/bootm.c
+++ b/arch/x86/lib/bootm.c
@@ -36,7 +36,7 @@
 	printf("\nStarting kernel ...\n\n");
 
 #ifdef CONFIG_SYS_COREBOOT
-	timestamp_add_now(TS_U_BOOT_START_KERNEL);
+	timestamp_add_now(TS_START_KERNEL);
 #endif
 	bootstage_mark_name(BOOTSTAGE_ID_BOOTM_HANDOFF, "start_kernel");
 #if CONFIG_IS_ENABLED(BOOTSTAGE_REPORT)