drm/i915/cnl: Fix, simplify and unify wrpll variable sizes.

- 64 bits is not needed for afe_clock now we don't convert
  that to Hz.
- 16 bits is not enough for all dco stuff.
- unsigned is not relevant/needed for all divisors values.

Cc: Mika Kahola <mika.kahola@intel.com>
Cc: Manasi Navare <manasi.d.navare@intel.com>
Cc: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Manasi Navare <manasi.d.navare@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171114194759.24541-4-rodrigo.vivi@intel.com