Move `get_attached_expansion` function to `BladeRF` trait

[QuantumEF]

While no expansion boards are sold for the BladeRf2.0 anymore (I think the XB100 was compatible, but discontinued), the expansion header for this still exists, so it is valid to call this function on the BladeRf2.0. Therefore, there is no need to constrain this function to the BladeRf1.

Also remember to update the docs for the ExpansionModule enum.