BACKPORT: dma-buf: cleanup dma_fence_unwrap implementation

Move the code from the inline functions into exported functions.

Change-Id: Ib0d156faa7270a9a2bb4124cfc781c0a2fea9752
Signed-off-by: Christian König <christian.koenig@amd.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518135844.3338-3-christian.koenig@amd.com


(cherry picked from commit 01357a5a)
[TJ: Cannot "nuke seqno-fence" due to stable KMI]
Bug: 394776841
Signed-off-by: T.J. Mercier <tjmercier@google.com>