drm/i915: Move the DPLL vfunc inits after the func defines

Move the per-platform DPLL and DPLL-manager vfunc initializations right
after the corresponding function definitions.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200226203455.23032-5-imre.deak@intel.com