net: thunderx: 80xx BGX0 configuration changes

On 80xx only one lane of DLM0 and DLM1 (of BGX0) can be used
, so even though lmac count may be 2 but LMAC1 should use
serdes lane of DLM1. Since it's not possible to distinguish
80xx from 81xx as PCI devid are same, this patch adds this
config support by replying on what firmware configures the
lmacs with.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>