Reference and PTP clocks rate of the Loongson GMAC devices is 125MHz.
(So is in the GNET devices which support is about to be added.) Set
the respective plat_stmmacenet_data field up in accordance with that
so to have the coalesce command and timestamping work correctly.

Fixes: 30bba69d ("stmmac: pci: Add dwmac support for Loongson")
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>