Refactor resource spp placement group and documentation

[Alexander-Kita]

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Relates OR Closes #0000

Output from acceptance testing:

=== RUN   TestAccIBMPISPPPlacementGroupBasic
--- PASS: TestAccIBMPISPPPlacementGroupBasic (1148.60s)
PASS

[ismirlia]

Can you sort this block as well

d.Set(Arg_CloudInstanceID, cloudInstanceID)
	d.Set(Arg_SPPPlacementGroupName, response.Name)
	d.Set(Attr_SPPPlacementGroupID, response.ID)
	d.Set(Arg_SPPPlacementGroupPolicy, response.Policy)
d.Set(Attr_SPPPlacementGroupMembers, response.MemberSharedProcessorPools)

[Alexander-Kita]

Opened: IBM-Cloud#5962