[util] FPGA resource utilisation reporting + visualiser utility

[thomas6785]

This PR provides utility scripts (TCL, Python, and bash) for generating FPGA resource utilisation.
Resource utilisation is not currently constrained but could be in future - it is also a useful proxy for what is costing build time, and generally useful for building an intuitive view of the design.

TCL generates a text report which is quite difficult to read. I have a Python script to parse this and generate sunburst charts like the below:

(You can click on a wedge in this diagram to zoom in and see its children in more detail)

I found this utility handy as a way of intuitively understanding the resource cost of certain blocks

Some notes

• This introduces Numpy and Plotly to the Python environment. These are both very popular and widely supported, but they are also quite "heavyweight" which may or may not be justified
• The bash script is a little fragile as it needs to be run from the repository root due to relative file paths. I'm not sure of a universally supported way of avoiding this problem
• Currently only generates sunbursts plots but many other visualisations are possible and potentially useful
• Currently only analyses resource utilisation but this flow (open project -> run TCL script -> post process in Python) is plausibly very useful for reporting CDC, DRCs, power, timing results, and maybe even bus latency or other performance criteria
• I would love to see a colour-coded diagram showing the physical implementation on FPGA regions. You can view this in the Vivado GUI but there is no mechanism for exporting as far as I know
• Only reports on the current build - would be nice to get a plot showing change over time to identify any changes that may otherwise go unnoticed
• This would be best implemented as a FuseSoC hook, but the docs on using those are currently three words: "TODO document hooks"

I most likely won't have time to address these issues/ideas as it is my last week with lowRISC, but documenting them here in case anybody finds them useful.

[marnovandermaas]

Some minor comments from my end. Any reason why this is still marked as draft? I would be happy to get this into the repository.