Change in coreboot[master]: util/spd_tools: Add support for exclusive IDs

[Karthik Ramasubramanian (Code Review)]

Attention is currently required from: Robert Zieba, Raul Rangel, Reka Norman, Nick Vaccaro.
Karthik Ramasubramanian has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/62905 )

Change subject: util/spd_tools: Add support for exclusive IDs
......................................................................

Patch Set 3:

(4 comments)

File util/spd_tools/src/part_id_gen/part_id_gen.go:

https://review.coreboot.org/c/coreboot/+/62905/comment/0a79a238_5f5986e1 
PS3, Line 96: mappingType
Do we need a new type

https://review.coreboot.org/c/coreboot/+/62905/comment/5e131021_f4230eb5 
PS3, Line 102: 
This can be:

const (
       Auto = iota
       Fixed
       Exclusive
)

https://review.coreboot.org/c/coreboot/+/62905/comment/9c3835fe_76f80c87 
PS3, Line 284: map[int]mappingType{}
Feels weird to use a map for the concerned use-case. Feels like an array is sufficient.

If planning to switch to array - extend the array along with partIdList as and when needed and initialize it as Auto.

https://review.coreboot.org/c/coreboot/+/62905/comment/df8e046d_bd5a1fca 
PS3, Line 314: if mapping, present := assignedMapping[p.index]; present {
             : 			// Don't allow explicit and non-explicit parts to use the same index
             : 			if mapping != p.mapping && (mapping == Exclusive || p.mapping == Exclusive) {
             : 				return nil, fmt.Errorf("Exclusive/non-exclusive conflict in assigning %s to ID %d", p.partName, p.index)
             : 			}
             : 		} else {
             : 			assignedMapping[p.index] = p.mapping
             : 		}
if planning to switch assignedMapping as array, this can be changed as:

```
if (assignedMapping[p.index] == Exclusive && p.mapping == Fixed) ||
   (assignedMapping[p.Index] == Fixed && p.mapping == Exclusive) {
        return nil, fmt.Errorf("...")
} else {
        assignedMapping[p.Index] = p.mapping
}
```