cmd/compile: move InitPlan and InitEntry into sinit.go

I don't know what they're used for, but that's the only file they're
referenced in.

Change-Id: Ie39d7d4621e2d5224408243b5789597ca0dc14be
Reviewed-on: https://go-review.googlesource.com/20593Reviewed-by: Dave Cheney <dave@cheney.net>

src/cmd/compile/internal/gc/go.go

@@ -99,18 +99,6 @@ type Label struct {
 	Used bool
 }
 
-type InitEntry struct {
-	Xoffset int64 // struct, array only
-	Expr    *Node // bytes of run-time computed expressions
-}
-
-type InitPlan struct {
-	Lit  int64
-	Zero int64
-	Expr int64
-	E    []InitEntry
-}
-
 type SymFlags uint8
 
 const (

src/cmd/compile/internal/gc/sinit.go

@@ -16,6 +16,18 @@ const (
 	InitPending    = 2
 )
 
+type InitEntry struct {
+	Xoffset int64 // struct, array only
+	Expr    *Node // bytes of run-time computed expressions
+}
+
+type InitPlan struct {
+	Lit  int64
+	Zero int64
+	Expr int64
+	E    []InitEntry
+}
+
 var (
 	initlist  []*Node
 	initplans map[*Node]*InitPlan