This is for callers who want micro-second precision but are not
waiting from the atomic context.
v2:
* Fix atomic waits. (Dave Gordon)
* Use USEC_PER_SEC and USEC_PER_MSEC. (Chris Wilson)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com> Cc: Dave Gordon <david.s.gordon@intel.com> Cc: Chris Wilson <chris@chris-wilson.co.uk> Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>