net: thunderx: Fix set_max_bgx_per_node for 81xx rgx

Add the PCI_SUBSYS_DEVID_81XX_RGX and use the same to set
the max bgx per node count.

This fixes the issue intoduced by following commit
78aacb6f

 net: thunderx: Fix invalid mac addresses for node1 interfaces
With this commit the max_bgx_per_node for 81xx is set as 2 instead of 3
because of which num_vfs is always calculated as zero.

Signed-off-by: George Cherian <george.cherian@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>