x86: Add a CBMEM timestamp generated right before the kernel startup.

To maintain the initialization state of the timestamp facility, thesq
pointer to the CBMEM section containing the timestamp table should be
kept in the .data section (so that it is maintained across u-boot
relocation).

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