drm/i915: make device info a const pointer to rodata

Finally we can get rid of the pseudo-const write-once device info, and
convert it into a const pointer to device info in rodata.

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/f31933222f44e4a9224e41399a96896eb243e653.1687878757.git.jani.nikula@intel.com