drm/i915: move chv_dpll_md and bxt_phy_grc to display sub-struct under state

Move the display related members to the struct drm_i915_private display
sub-struct. Put them under "state", as they are related to storing
values that aren't readable from the hardware, to appease the state
checker.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230117143946.2426043-3-jani.nikula@intel.com