drm/i915: add dpll_info inside intel_shared_dpll

This way we can stop copying fields from dpll_info to intel_shared_dpll
one by one. The migration of each field will come on separate patches.

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/20180320220637.21480-3-lucas.demarchi@intel.com