cmd/compile: change ir.NewCompLitExpr from Ntype to *types.Type

cmd/compile: change ir.NewCompLitExpr from Ntype to *types.Type

All callers were already using TypeNode to get an Ntype anyway, so
just push the TypeNode constructor down into NewCompLitExpr. Prep
refactoring for next CL to remove the Ntype field.

Change-Id: I671935afca707aaab11d1c46e39902bd37a485ba
Reviewed-on: https://go-review.googlesource.com/c/go/+/403840
Run-TryBot: Matthew Dempsky <mdempsky@google.com>
TryBot-Result: Gopher Robot <gobot@golang.org>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Cuong Manh Le <cuong.manhle.vn@gmail.com>