drm/ttm: add ttm_bo_pin()/ttm_bo_unpin() v2

[ Upstream commit deb0814b ]

As an alternative to the placement flag add a
pin count to the ttm buffer object.

v2: add dma_resv_assert_help() calls

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Huang Rui <ray.huang@amd.com>
Link: https://patchwork.freedesktop.org/patch/391596/?series=81973&rev=1


Stable-dep-of: a2848d08 ("drm/ttm: never consider pinned BOs for eviction&swap")
Signed-off-by: Sasha Levin <sashal@kernel.org>