nova/flavors: Use fewest-possible sockets for 64vcpu+

[grandchild]

Windows images have a socket limitation of 64, as hinted here: https://learn.microsoft.com/en-us/archive/msdn-technet-forums/56adf991-952e-4337-8159-d632499db22b

Also, non-server windows images have even lower limits (2 or 4 sockets).

For all regular flavors with 64 vCPUS and more, set the cores-per-socket value to the vCPU/socket value of our (Cascade-Lake) hardware.