cmd/compile: ppc64x no longer needs a scratch stack location

After https://go-review.googlesource.com/c/36725/, ppc64x no longer
needs a temp stack location for int reg <-> fp reg moves.

Update #18922

Change-Id: Ib4319784f7a855f593dfa5231604ca2c24e4c882
Reviewed-on: https://go-review.googlesource.com/37651Reviewed-by: Lynn Boger <laboger@linux.vnet.ibm.com>

src/cmd/compile/internal/ssa/config.go

@@ -221,7 +221,6 @@ func NewConfig(arch string, fe Frontend, ctxt *obj.Link, optimize bool) *Config
 		c.FPReg = framepointerRegPPC64
 		c.LinkReg = linkRegPPC64
 		c.noDuffDevice = true // TODO: Resolve PPC64 DuffDevice (has zero, but not copy)
-		c.NeedsFpScratch = true
 		c.hasGReg = true
 	case "mips64":
 		c.BigEndian = true

src/cmd/compile/internal/ssa/gen/PPC64Ops.go

@@ -211,8 +211,8 @@ func init() {
 		// There are optimizations that should apply -- (Xi2f64 (MOVWload (not-ADD-ptr+offset) ) ) could use
 		// the word-load instructions.  (Xi2f64 (MOVDload ptr )) can be (FMOVDload ptr)
 
-		{name: "Xf2i64", argLength: 1, reg: fpgp, typ: "Int64", usesScratch: true},   // move 64 bits of F register into G register
-		{name: "Xi2f64", argLength: 1, reg: gpfp, typ: "Float64", usesScratch: true}, // move 64 bits of G register into F register
+		{name: "Xf2i64", argLength: 1, reg: fpgp, typ: "Int64"},   // move 64 bits of F register into G register
+		{name: "Xi2f64", argLength: 1, reg: gpfp, typ: "Float64"}, // move 64 bits of G register into F register
 
 		{name: "AND", argLength: 2, reg: gp21, asm: "AND", commutative: true},               // arg0&arg1
 		{name: "ANDN", argLength: 2, reg: gp21, asm: "ANDN"},                                // arg0&^arg1

src/cmd/compile/internal/ssa/opGen.go

@@ -16421,7 +16421,6 @@ var opcodeTable = [...]opInfo{
 	{
 		name:   "Xf2i64",
 		argLen: 1,
-		usesScratch: true,
 		reg: regInfo{
 			inputs: []inputInfo{
 				{0, 576460743713488896}, // F1 F2 F3 F4 F5 F6 F7 F8 F9 F10 F11 F12 F13 F14 F15 F16 F17 F18 F19 F20 F21 F22 F23 F24 F25 F26
@@ -16434,7 +16433,6 @@ var opcodeTable = [...]opInfo{
 	{
 		name:   "Xi2f64",
 		argLen: 1,
-		usesScratch: true,
 		reg: regInfo{
 			inputs: []inputInfo{
 				{0, 1073733624}, // R3 R4 R5 R6 R7 R8 R9 R10 R11 R12 R14 R15 R16 R17 R18 R19 R20 R21 R22 R23 R24 R25 R26 R27 R28 R29