drm/i915/lvds: Extract intel_lvds_regs.h

Extract the integrated LVDS port register definitions
into their own header file.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130180540.8972-5-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>