cpu/intel: Use the common code to initialize the romstage timestamps

The initial timestamps are now pushed on the stack when entering the
romstage C code.

Tested on Asus P5QC.

Change-Id: I88e972caafff5c53d8e68e85415f920c7341b92d
Signed-off-by: Arthur Heymans <arthur@aheymans.xyz>
Reviewed-on: https://review.coreboot.org/c/30670
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>

src/northbridge/intel/sandybridge/romstage.c

@@ -53,9 +53,6 @@ void mainboard_romstage_entry(unsigned long bist)
 		halt ();
 	}
 
-	timestamp_init(get_initial_timestamp());
-	timestamp_add_now(TS_START_ROMSTAGE);
-
 	if (bist == 0)
 		enable_lapic();