Change in coreboot[master]: ACPI: Declare GNVS variables globally

[Tim Wawrzynczak (Code Review)]

Attention is currently required from: Lance Zhao, Jason Glenesk, Mariusz Szafrański, Marshall Dawson, Suresh Bellampalli, Vanessa Eusebio, Patrick Rudolph, Michal Motyl, Kyösti Mälkki, Andrey Petrov, Felix Held.
Tim Wawrzynczak has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/49795 )

Change subject: ACPI: Declare GNVS variables globally
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Patch Set 5: Code-Review+2

(1 comment)

File src/acpi/acpigen_extern.asl:

https://review.coreboot.org/c/coreboot/+/49795/comment/40f8cf0d_e862c1b4 
PS3, Line 11: External (NVB0, IntObj)
> I don't follow your comment about spec only mentioning MethodObj. […]

The 6.3 spec also says (19.6.44 External (Declare External Objects)):
```
ObjectType is an optional ObjectTypeKeyword (e.g. IntObj, PkgObj, etc.). If not specified, “UnknownObj” type is assumed.`
```
which would seem to imply that any ObjectType is OK.