drm/i915: Nuke pointless div by 64bit

Bunch of places use a 64bit divisor needlessly. Switch
to 32bit divisor.

Cc: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200302143943.32676-1-ville.syrjala@linux.intel.com
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>