CVE-2023-52913

In the Linux kernel, the following vulnerability has been resolved:

drm/i915: Fix potential context UAFs

gem_context_register() makes the context visible to userspace, and which
point a separate thread can trigger the I915_GEM_CONTEXT_DESTROY ioctl.
So we need to ensure that nothing uses the ctx ptr after this.  And we
need to ensure that adding the ctx to the xarray is the *last* thing
that gem_context_register() does with the ctx pointer.

[tursulin: Stable and fixes tags add/tidy.]
(cherry picked from commit bed4b455cf5374e68879be56971c1da563bcd90c)