Change in coreboot[master]: drivers/intel/gma: Restructure IGD opregion init code

[Angel Pons (Code Review)]

Attention is currently required from: Nico Huber, Furquan Shaikh, Maulik V Vaghela, Tim Wawrzynczak.
Angel Pons has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/55318 )

Change subject: drivers/intel/gma: Restructure IGD opregion init code
......................................................................

Patch Set 3: Code-Review+2

(2 comments)

File src/drivers/intel/gma/opregion.c:

https://review.coreboot.org/c/coreboot/+/55318/comment/63858a0c_225f4aed 
PS2, Line 321: we need
> It's requirement of OPREGION 2.1 spec as it expects extended VBT to sit at 8 KiB offset. […]

Is the OpRegion 2.1 specification publicly available?

https://review.coreboot.org/c/coreboot/+/55318/comment/493adddf_4418d0d8 
PS2, Line 327: 	opregion = cbmem_add(CBMEM_ID_IGD_OPREGION, opregion_size);
> sure...Let me split the patch into 2.

Thanks!