timekeeping: Get rid of pointless typecasts

cycle_t is defined as u64, so casting it to u64 is a pointless and
confusing exercise. cycle_t should simply go away and be replaced with a
plain u64 to avoid further confusion.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Parit Bhargava <prarit@redhat.com>
Cc: Laurent Vivier <lvivier@redhat.com>
Cc: "Christopher S. Hall" <christopher.s.hall@intel.com>
Cc: Chris Metcalf <cmetcalf@mellanox.com>
Cc: Richard Cochran <richardcochran@gmail.com>
Cc: Liav Rehana <liavr@mellanox.com>
Cc: John Stultz <john.stultz@linaro.org>
Link: http://lkml.kernel.org/r/20161208204228.844699737@linutronix.de
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>