drm/i915: use flags from dpll_info embedded in intel_shared_dpll

Replace all users of pll->flags to use pll->info.flags.

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/20180320220637.21480-7-lucas.demarchi@intel.com