e100: timer power saving

Since E100 timer is 2HZ, use rounding to make timer occur on the
correct boundary.

Signed-off-by: Stephen Hemminger <shemminger@linux-foundation.org>
Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
Signed-off-by: Jeff Garzik <jeff@garzik.org>