Change in coreboot[master]: soc/intel/graphics: Create Kconfig for mapping graphic memory base

[Wonkyu Kim (Code Review)]

Attention is currently required from: Nico Huber, Subrata Banik, 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: Create Kconfig for mapping graphic memory base
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Patch Set 17:

(1 comment)

File src/soc/intel/common/block/graphics/graphics.c:

https://review.coreboot.org/c/coreboot/+/61389/comment/e80b7cdb_3c84ba87 
PS13, Line 128: memory_base = memory_base + CONFIG_SOC_INTEL_GFX_MEMBASE_OFFSET;
> > GTT size is considered in CONFIG_SOC_INTEL_GFX_MEMBASE_OFFSET. […]

We checked GFX team and found that GFX need to use fixed GTT size for new platform while current FSP has UPD for GTT size.   After we internal sync up, we got info that  FSP will be updated (remove upd for gtt size)
So, current constant offset should be ok.