drm/i915: use funcs from intel_shared_dpll.info

Replace all users of pll->funcs.* to use
pll->info->funcs->*. The extra indirection here is not on any critical
path and we can leave all const data together.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180320220637.21480-4-lucas.demarchi@intel.com