drm/i915/gt: drop dependency on VLV_DISPLAY_BASE

CHV_FUSE_GT (0x182168) is purely about GT fuses, therefore belongs in
intel_gt_regs.h, is in the gcfgmmio unit, but is technically in the VLV
display base area.

Add VLV_GUNIT_BASE to drop dependency on VLV_DISPLAY_BASE and thus
display/intel_display_reg_defs.h in intel_gt_regs.h.

v2: Add VLV_GUNIT_BASE (Ville)

Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230511152153.986676-1-jani.nikula@intel.com