drm/i915/bios: amend child device config parameters

Add both some new and some old fields to child device config
parameters. Prepare for switching to just one child device config. Use
naming from struct old_child_dev_config for common fields.

No functional changes.

Cc: Animesh Manna <animesh.manna@intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/bbf66c934eb5c655fd7dda6c1bb8f218c8edc209.1503600621.git.jani.nikula@intel.com