drm/amdgpu: add the interface of waiting multiple fences (v4)

v2: agd: rebase and squash in all the previous optimizations and
changes so everything compiles.
v3: squash in Slava's 32bit build fix
v4: rebase on drm-next (fence -> dma_fence),
    squash in Monk's ioctl update patch

Signed-off-by: Junwei Zhang <Jerry.Zhang@amd.com>
Reviewed-by: Monk Liu <monk.liu@amd.com>
Reviewed-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Sumit Semwal <sumit.semwal@linaro.org>
 [sumits: fix checkpatch warnings]
Link: http://patchwork.freedesktop.org/patch/msgid/1478290570-30982-2-git-send-email-alexander.deucher@amd.com