net: stmmac: Move the atds flag to the stmmac_dma_cfg structure

ATDS (Alternate Descriptor Size) is a part of the DMA Bus Mode configs
(together with PBL, ALL, EME, etc) of the DW GMAC controllers. Seeing
it's not changed at runtime but is activated as long as the IP-core
has it supported (at least due to the Type 2 Full Checksum Offload
Engine feature), move the respective parameter from the
stmmac_dma_ops::init() callback argument to the stmmac_dma_cfg
structure, which already have the rest of the DMA-related configs
defined.

Besides the being added in the next commit DW GMAC multi-channels
support will require to add the stmmac_dma_ops::init_chan() callback
and have the ATDS flag set/cleared for each channel in there. Having
the atds-flag in the stmmac_dma_cfg structure will make the parameter
accessible from stmmac_dma_ops::init_chan() callback too.

Signed-off-by: Feiyang Chen <chenfeiyang@loongson.cn>
Signed-off-by: Yinggang Gu <guyinggang@loongson.cn>
Reviewed-by: Serge Semin <fancer.lancer@gmail.com>
Acked-by: Huacai Chen <chenhuacai@loongson.cn>
Signed-off-by: Yanteng Si <siyanteng@loongson.cn>
Tested-by: Serge Semin <fancer.lancer@gmail.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>