cmd/compile: start MIPS64 port of SSA backend

Fib with all int and float types run correctly.
*, /, shifts, Zero, Move not implemented yet. No optimization yet.

Updates #16359.

Change-Id: I4b0412954d5fd4c13a5fcddd8689ed8ac701d345
Reviewed-on: https://go-review.googlesource.com/27404
Reviewed-by: David Chase <drchase@google.com>

Author: cherrymui

src/cmd/compile/internal/mips64/galign.go

@@ -6,6 +6,7 @@ package mips64
 
 import (
 	"cmd/compile/internal/gc"
+	"cmd/compile/internal/ssa"
 	"cmd/internal/obj"
 	"cmd/internal/obj/mips"
 )
@@ -62,6 +63,11 @@ func Main() {
 	gc.Thearch.Doregbits = doregbits
 	gc.Thearch.Regnames = regnames
 
+	gc.Thearch.SSARegToReg = ssaRegToReg
+	gc.Thearch.SSAMarkMoves = func(s *gc.SSAGenState, b *ssa.Block) {}
+	gc.Thearch.SSAGenValue = ssaGenValue
+	gc.Thearch.SSAGenBlock = ssaGenBlock
+
 	gc.Main()
 	gc.Exit(0)
 }