drm/amdgpu: allow pinning DMA-bufs into VRAM if all importers can do P2P

Try pinning into VRAM to allow P2P with RDMA NICs without ODP
support if all attachments can do P2P. If any attachment can't do
P2P just pin into GTT instead.

Acked-by: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Felix Kuehling <felix.kuehling@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Tested-by: Pak Nin Lui <pak.lui@amd.com>
Cc: Simona Vetter <simona.vetter@ffwll.ch>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>