Add Verilog files for FPGA/Misc/PTMClock package

[quark17]

The PTMClock package imports two Verilog modules that were still in the BSC repo and had accidentally not been migrated here. (They were removed from the BSC repo in B-Lang-org/bsc#388.)

This repo had not yet been installing any Verilog files, and I had to add a mechanism for storing and installing them. The current structure of this repo mirrors what the BSC repo does, where the library sources are in one (possibly interdependent) tree and the Verilog is in a separate tree. I would prefer that this repo be structured by project, keeping the source and Verilog (and docs and scripts and any other files) together. But for now I've just continued to mirror what the BSC repo does.