Change in coreboot[master]: soc/intel/graphics: Add override api for graphics_get_memory_base()

[Wonkyu Kim (Code Review)]

Attention is currently required from: Subrata Banik, Nico Huber, Ethan Tsao, Ravishankar Sarawadi, Tim Wawrzynczak, Paul Menzel, Raj Astekar, Patrick Rudolph.
Wonkyu Kim has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/61389 )

Change subject: soc/intel/graphics: Add override api for graphics_get_memory_base()
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Patch Set 8:

(1 comment)

Patchset:

PS7:
> > > In future platform, PCI config 0x18 still has memory bar but display memory may not same as memo […]

In future platform, PCI config 0x18 still has memory bar but display memory may not same as memory bar address.
=> Yes, it'll be in between with offsets.

Exactly, I also have the same question and if that offset/address is still as part of PCI configuration space, can't we use a Kconfig (select from SoC) and common code take care of passing the address from *new offset*. I really don't think we need SoC override.

=> The concern is the fixed offset can not cover all the case like below.
ex)
display memory = PCI config 0x18 + GTT size + fixed offset

GTT size can be updated based on UPD.  
In that case using Kconfig offset can't support for different GTT size.

That's reason why we want to override function to make more flexible.