drm/i915/dg2: Drop pre-production GT workarounds

From Matt Roper
0a9901fdb7bb785ec4975aeeebc1428e3abae172 in linux-6.6.y/6.6.26
eaeb4b3614529bfa8a7edfdd7ecf6977b27f18b2 in mainline linux

update drm to linux 6.6.12

Thanks to the OpenBSD Foundation for sponsoring this work.