drm/i915/perf: Treat u64 in uabi as a normal integer

drm/i915/perf: Treat u64 in uabi as a normal integer

Forgo marking up the u64 integer representing a user pointer as this
just annoys sparse. The conversion from u64 to a user pointer is managed
by u64_to_user_ptr().

Fixes: b3eb6faf8152 ("drm/i915: Add i915 perf infrastructure")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Robert Bragg <robert@sixbynine.org>
Cc: Matthew Auld <matthew.auld@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20161130164649.26809-1-chris@chris-wilson.co.uk
Reviewed-by: Matthew Auld <matthew.auld@intel.com>