drm/i915: Align the hangcheck wakeup to the nearest second

round_jiffies() aligns the wakeup time to the nearest second in order to
batch wakeups and reduce system load, which is useful for unimportant
coarse timers like our hangcheck.

v2: round_jiffies_relative() returns the relative jiffie value, whereas
we need the absolute value for the timer.

Suggested-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>