Change library structure to allow ipbus-firmware to be compiled into a separate library

[pfindlay-cern]

I've added an explicit library xil_defaultlib to all files that use xilinx IP. See https://adaptivesupport.amd.com/s/question/0D52E00006iHs8USAS/changing-ip-library-in-vivado?language=en_US. Where the work library was being used to access entity instantiations of Xilinx IP this is updated to use xil_defaultlib instead.

This change allows compilation of the ipbus firmware into its own library. It is not possible to selectively compile Xilinx IP into different libraries. All IPs are compiled into the project's default library.

Could potentially causes issues for any project that:

• Is using a version of Vivado older than 2014.1.
• Has changed the default compilation library in Vivado.