drm/i915: use display snapshot mechanism for display irq regs

Move more display specific parts of GPU error logging behind the display
snapshot interface.

With the display register capture reduced to just one register, DERRMR,
there's quite a bit of boilerplate here. However, it's still a nice
abstraction and removes a DISPLAY_VER() usage from core i915. With this
approach, it's also easy to add to xe as needed.

v2: Remove stale comment

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/13206969df04426d290d2863dc574e22ca45193a.1744630147.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>