timestamps intel: Move timestamp scratchpad to chipset

This retrieves back the value stored with store_initial_timestamp()
in the bootblock for southbridge.

Change-Id: I377c823706c33ed65af023d20d2e4323edd31199
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/3908
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
Reviewed-by: Aaron Durbin <adurbin@google.com>

src/include/timestamp.h

@@ -61,6 +61,7 @@ void timestamp_add(enum timestamp_id id, tsc_t ts_time);
 void timestamp_add_now(enum timestamp_id id);
 void timestamp_stash(enum timestamp_id id);
 void timestamp_sync(void);
+tsc_t get_initial_timestamp(void);
 #else
 #define timestamp_init(base)
 #define timestamp_add(id, time)