I/OAT: tcp_dma_copybreak default value dependent on I/OAT version

I/OAT DMA performance tuning showed different optimal values of
tcp_dma_copybreak for different I/OAT versions (4096 for 1.2 and 2048
for 2.0).  This patch lets ioatdma driver set tcp_dma_copybreak value
according to these results.

[dan.j.williams@intel.com: remove some ifdefs]
Signed-off-by: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>