UPSTREAM: dma-buf: Add dma_fence_array_for_each (v2)

Add a helper to iterate over all fences in a dma_fence_array object.

v2 (Jason Ekstrand)
 - Return NULL from dma_fence_array_first if head == NULL.  This matches
   the iterator behavior of dma_fence_chain_for_each in that it iterates
   zero times if head == NULL.
 - Return NULL from dma_fence_array_next if index > array->num_fences.

Bug: 310208240
Change-Id: Ic142d9066c8ed14fd1ca7163f8ac5eaf15c6d972
Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Reviewed-by: Christian König <christian.koenig@amd.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210610210925.642582-2-jason@jlekstrand.net


Signed-off-by: Christian König <christian.koenig@amd.com>
(cherry picked from commit caaf2ae7)
Signed-off-by: Richard Fung <richardfung@google.com>