Add a new flag to let userspace provide a deadline as a hint for syncobj
and timeline waits.  This gives a hint to the driver signaling the
backing fences about how soon userspace needs it to compete work, so it
can adjust GPU frequency accordingly.  An immediate deadline can be
given to provide something equivalent to i915 "wait boost".

v2: Use absolute u64 ns value for deadline hint, drop cap and driver
    feature flag in favor of allowing count_handles==0 as a way for
    userspace to probe kernel for support of new flag
v3: More verbose comments about UAPI
v4: Fix negative zero, s/deadline_ns/deadline_nsec/ for consistency with
    existing ioctl struct fields
v5: Comment/description typo fixes
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
[DB: fixed checkpatch warnings]
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230823215458.203366-2-robdclark@gmail.com