We need to use the clock control reg to figure out how many CZ clks are in
30ns and use that as the basis for our RC6 residency calculations.

v2: use ULL everywhere for consistency (Chris)
    factor out bias for clarity (Chris)

References: https://bugs.freedesktop.org/show_bug.cgi?id=69692Signed-off-by: NJesse Barnes <jbarnes@virtuousgeek.org>
Reviewed-by: NChris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>