drm/i915/perf: Wrap 64bit divides in do_div()

Just a couple of naked 64bit divides causing link errors on 32bit
builds, with:

	ERROR: "__udivdi3" [drivers/gpu/drm/i915/i915.ko] undefined!

v2: do_div() is only u64/u32, we need a u32/u64!
v3: div_u64() == u64/u32, div64_u64() == u64/u64

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Fixes: d7965152 ("drm/i915: Enable i915 perf stream for Haswell OA unit")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Robert Bragg <robert@sixbynine.org>
Link: http://patchwork.freedesktop.org/patch/msgid/20161123150714.24449-1-chris@chris-wilson.co.uk


Reviewed-by: Robert Bragg <robert@sixbynine.org>