Split docs/rules/layers/table-c4b-layer-description.csv into three tables

It seems like the [`docs/rules/layers/table-c4b-layer-description.csv`](https://github.com/google/skywater-pdk/blob/master/docs/rules/layers/table-c4b-layer-description.csv) file should be split into three separate tables.

_Originally posted by @mithro in https://github.com/google/skywater-pdk/pull/127#r486749885_