dma-buf/sw-sync: sync_pt is private and of fixed size

Since sync_pt is only allocated from a single location and is no longer
the base class for fences (that is struct dma_fence) it no longer needs
a generic unsized allocator.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Sumit Semwal <sumit.semwal@linaro.org>
Cc: Sean Paul <seanpaul@chromium.org>
Cc: Gustavo Padovan <gustavo@padovan.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170629125930.821-5-chris@chris-wilson.co.uk