LUTTools.swapSingleLutPins() cannot swap H[1-6] when used as WA

[eddieh-xlnx]

Currently, LUT pin swapping features added in #894 can only cope with a single pair of LUTs. In SLICEMs, the LUT pins H[1-6] also serve as the WA (write address) for distributed RAM across LUTs [A-G], and so any pin swaps requires modifying more than just a pair of cell pin mappings.