perf tools: Move timestamp routines from util.h to time-utils.h

We already have a header for time utilities, so use it.

Link: http://lkml.kernel.org/n/tip-sijzpbvutlg0c3oxn49hy9ca@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>