dma-fence: Add helper to sort and deduplicate dma_fence arrays

Export a new helper function `dma_fence_dedup_array()` that sorts
an array of dma_fence pointers by context, then deduplicates the array
by retaining only the most recent fence per context.

This utility is useful when merging or optimizing sets of fences where
redundant entries from the same context can be pruned. The operation is
performed in-place and releases references to dropped fences using
dma_fence_put().

v2: - Export this code from dma-fence-unwrap.c(by Christian).
v3: - To split this in a dma_buf patch and amd userq patch(by Sunil).
    - No need to add a new function just re-use existing(by Christian).
v4: - Export dma_fence_dedub_array and use it(by Christian).

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Arunpravin Paneer Selvam <Arunpravin.PaneerSelvam@amd.com>
Reviewed-by: Sunil Khatri <sunil.khatri@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Arvind Yadav <Arvind.Yadav@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>