UPSTREAM: dma-buf: add dma_fence_chain_alloc/free v3

Add a common allocation helper. Cleaning up the mix of kzalloc/kmalloc
and some unused code in the selftest.

v2: polish kernel doc a bit
v3: polish kernel doc even a bit more

Change-Id: I66a85ce4763f9bb3923b00b01f840f873abc7cc5
Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20210611120301.10595-3-christian.koenig@amd.com


(cherry picked from commit 440d0f12)
Bug: 394776841
Signed-off-by: T.J. Mercier <tjmercier@google.com>