7x device mesh fall back to unoptimized when needed
Without this change creating a mesh of 32 devices out of 64 devices fails on v7x-64. The following error will be seen:
```
JAX device count: 64
Using 32 devices for the mesh.
Attempting jax.make_mesh((1, 32), ('fsdp', 'tp'))
AssertionError: Unexpected physical mesh shape: (2, 4, 2, 2).
```
PiperOrigin-RevId: 828008412
