drm: Add DRM prime interface to reassign GEM handle

drm: Add DRM prime interface to reassign GEM handle

CRIU restore of drm buffer objects requires the ability to create
or import a buffer object with a specific gem handle.

Add new drm ioctl DRM_IOCTL_GEM_CHANGE_HANDLE, which takes
the gem handle of an object and moves that object to a
specified new gem handle.

This ioctl needs to call drm_prime_remove_buf_handle,
but that function acquires the prime lock, which the ioctl
needs to hold for other purposes.

Make drm_prime_remove_buf_handle not acquire the prime lock,
and change its other caller to reflect this.

The rest of the kernel patches required to enable CRIU can be
found at
https://lore.kernel.org/dri-devel/20250617194536.538681-1-David.Francis@amd.com/

v2 - Move documentation to UAPI headers
v3 - Always return 0 on success

Signed-off-by: David Francis <David.Francis@amd.com>
Acked-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Christian König <christian.koenig@amd.com>
Link: https://lore.kernel.org/r/20250717143556.857893-2-David.Francis@amd.com