This patch adds a new ioctl GEM_CHANGE_HANDLE which is needed by amdgpu CRIU for dmabuf.
The ioctl allows a user to move a gem object to a new handle. v2: Move documentation for this and other drm_gem ioctls to drm.h v3: After testing with IGT, fixed return value on success Accompanying changes: kernel (for dmabuf CRIU support) https://lists.freedesktop.org/archives/dri-devel/2025-June/510996.html igt (for this ioctl) https://gitlab.freedesktop.org/fdavid-amd/igt-gpu-tools CRIU (for dmabuf CRIU support) https://github.com/checkpoint-restore/criu/pull/2613
