x86: Enable coreboot timestamp facility support in u-boot.

This change turns on the code which allows u-boot to add
timestamps to the timestamp table created by coreboot.

Since u-boot does not use the tsc_t like structure to represent
HW counter readings, this structure is being replaced by 64 bit
integer.

The timestamp_init() function is now initializing the base timer
value used by u-boot to calculate the HW counter increments.

Timestamp facility is initialized as soon as the timestamp table
pointer is found in the coreboot table. The u-boot generated
timer events' ID will start at 1000 to clearly separate u-boot
events from coreboot events in the timer trace.

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Signed-off-by: Stefan Reinauer <reinauer@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>