The genvar stuff was switched to readable names to make it easier
to understand for the first time. In the LRUUpdate logic for loop,
a special case was added for simpler logic in the case of the root
node, to hit coverage.
For coverage.
LRUWriteEn is gated by FlushStage in cache.sv,
so removing the signal completely avoids future confusion.
Update cache.sv to reflect cacheLRU edit.
