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. In this version, I have added kerneldoc comments for the new ioctl in drm.h and have moved over the other drm_gem.c ioctl docs to drm.h. Accompanying changes: kernel (for dmabuf CRIU support) https://lore.kernel.org/dri-devel/20250617194536.538681-1-david.fran...@amd.com/ 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
