PCIe build warnings from devicetree

[ghost]

Describe the bug

When building targets with PCIe devices in devicetree, warnings are produced that need to be silenced.

To Reproduce
Steps to reproduce the behavior:

1. mkdir build; cd build
2. cmake -DBOARD=up_squared
3. make
4. See warnings like up_squared.dts.pre.tmp:94.15-105.5: Warning (simple_bus_reg): /soc/i2c@1: simple-bus unit address format error, expected "b100"

Impact
It's an annoyance (and bad form).

[ghost]

@galak and @ulfalizer are rewriting the devicetree scripts. Waiting on that before I fix this.

[ghost]

Changed to medium-priority bug to be sure this stays on our radar for 2.0 release.

Now that the new devicetree scripts are in place I can proceed to fix properly.

[galak]

@gnuless can we leave this as low, I don't think we're going to fix / address this in the 2.0.0 timeframe.

[ioannisg]

@gnuless pls, give it a try if you have time :p

[ghost]

@galak @ioannisg I'm going to try to get a PR in for this this week. With the new DT scripts in place, I'm getting pagefulls of warnings during the configuration process for any platform that uses PCIe devices, and that's just really, really bad form.

[ghost]

@galak is right, it's going to take longer than we have to get all the changes integrated, so moving to 2.1.0 and changing back to low.

[ghost]

@galak can you revisit this now that the devicetree stuff has been rewritten? the new Python scripts double the number of warnings spewed during the configuration process. I'm really not sure I want to start tinkering with work-in-progress devicetree code, but I imagine restructuring the .dts files and emitting b/d/f for PCI devices can't be all that hard.