cmd/internal/obj: switch to one global Aconv

Aconv is the pretty-printer for instruction opcodes like AMOVQ.
There was one for each architecture.
Make the space of A names have a different region for each architecture,
much as we did for the registers, so a single global Aconv function can
do the work. Each architecture registers its region as a slice of names
at a given offset.

The global names like CALL and JMP are now defined only once.

The A values are used for indexing tables, so make it easy to do the
indexing by making the offset maskable.

Remove a bunch of now-duplicated architecture-specific code.

Change-Id: Ib15647b7145a1c089e21e36543691a19e146b60e
Reviewed-on: https://go-review.googlesource.com/6620
Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Rob Pike <r@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/cmd/internal/obj/link.go

@@ -424,6 +424,10 @@ const (
 // These are the portable opcodes, common to all architectures.
 // Each architecture defines many more arch-specific opcodes,
 // with values starting at A_ARCHSPECIFIC.
+// Each architecture adds an offset to this so each machine has
+// distinct space for its instructions. The offset is a power of
+// two so it can be masked to return to origin zero.
+// See the definitions of ABase386 etc.
 const (
 	AXXX = 0 + iota
 	ACALL
@@ -570,30 +574,4 @@ const (
 	LinkExternal
 )
 
-// asm5.c
-
-// asm6.c
-
-// asm8.c
-
-// asm9.c
-
-// data.c
-
-// go.c
-
-// ld.c
-
-// list[5689].c
-
-// obj.c
-
-// objfile.c
-
-// pass.c
-
-// pcln.c
-
-// sym.c
-
 var linkbasepointer int