all: power64 is now ppc64

Fixes #8654.

LGTM=austin
R=austin
CC=golang-codereviews
https://golang.org/cl/180600043
diff --git a/test/nosplit.go b/test/nosplit.go
index 3a63e87..d90cb9e 100644
--- a/test/nosplit.go
+++ b/test/nosplit.go
@@ -127,7 +127,7 @@
 # Calling a nosplit function from a nosplit function requires
 # having room for the saved caller PC and the called frame.
 # Because ARM doesn't save LR in the leaf, it gets an extra 4 bytes.
-# Because Power64 doesn't save LR in the leaf, it gets an extra 8 bytes.
+# Because ppc64 doesn't save LR in the leaf, it gets an extra 8 bytes.
 main 112 nosplit call f; f 0 nosplit
 main 116 nosplit call f; f 0 nosplit
 main 120 nosplit call f; f 0 nosplit; REJECT amd64
@@ -139,7 +139,7 @@
 # Calling a splitting function from a nosplit function requires
 # having room for the saved caller PC of the call but also the
 # saved caller PC for the call to morestack.
-# Again the ARM and Power64 work in less space.
+# Again the ARM and ppc64 work in less space.
 main 104 nosplit call f; f 0 call f
 main 108 nosplit call f; f 0 call f
 main 112 nosplit call f; f 0 call f; REJECT amd64
@@ -237,7 +237,7 @@
 		var buf bytes.Buffer
 		ptrSize := 4
 		switch goarch {
-		case "power64", "power64le":
+		case "ppc64", "ppc64le":
 			ptrSize = 8
 			fmt.Fprintf(&buf, "#define CALL BL\n#define REGISTER (CTR)\n#define RET RETURN\n")
 		case "arm":