Add CHANGE_HANDLE ioctl for drm gem v2

[David Francis]

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.Francis@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