[L] Change in coreboot[master]: mb/dell: Add OptiPlex 7020/9020 port

[Michael Büchler (Code Review)]

Attention is currently required from: Angel Pons, Michał Żygowski, Máté Kukri, Stefan Reinauer.

Michael Büchler has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/55232?usp=email )

Change subject: mb/dell: Add OptiPlex 7020/9020 port
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Patch Set 25: Code-Review+1

(2 comments)

Patchset:

PS25: 
Thank you for your work on this port! I tested this on a 9020 mini tower (MT). See my comment on the PCI(e) slots. Except that, all seems to work, but I did not test extensively. It boots with both a Haswell and a Broadwell mrc.bin.

I hope it's okay to give it a +1 as a non-regular contributor.

File src/mainboard/dell/optiplex_9020/devicetree.cb:

https://review.coreboot.org/c/coreboot/+/55232/comment/5a231d7c_6001ad7d :
PS25, Line 39: 			device pci 1c.1 off end
             : 		
The mini tower (MT) variant has two additional slots compared to the UFF variant:
* 1c.1: PCI (through a bridge chip: Texas Instruments XIO2001)
* 1c.2: PCIe x1

I enabled the two marked devices for a local build and both slots then work. Maybe introduce variants with an overridetree.cb?