cmd/internal/obj: support arm64 FMOVQ large offset encoding

Support arm64 FMOVQ with large offset in immediate which is encoded
using register offset instruction in opldrr or opstrr. This will help
allowing folding immediate into new ssa ops FMOVQload and FMOVQstore.

For example: FMOVQ F0, -20000(R0) is encoded as following:
  MOVD 3(PC), R27
  FMOVQ F0, (R0)(R27)
  RET
  ffff b1e0 # constant value

Change-Id: Ib71f92f6ff4b310bda004a440b1df41ffe164523
Reviewed-on: https://go-review.googlesource.com/c/go/+/716960
Reviewed-by: Cherry Mui <cherryyz@google.com>
Auto-Submit: Michael Pratt <mpratt@google.com>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Michael Pratt <mpratt@google.com>

Author: amusman

src/cmd/asm/internal/asm/testdata/arm64.s

@@ -630,6 +630,8 @@ TEXT	foo(SB), DUPOK|NOSPLIT, $-8
 	FMOVS	F1, 0x44332211(R2)	// FMOVS	F1, 1144201745(R2)
 	FMOVD	F1, 0x1007000(R2)	// FMOVD	F1, 16805888(R2)
 	FMOVD	F1, 0x44332211(R2)	// FMOVD	F1, 1144201745(R2)
+	FMOVQ	F1, 0x1003000(R2)	// FMOVQ	F1, 16789504(R2)
+	FMOVQ	F1, 0x44332211(R2)	// FMOVQ	F1, 1144201745(R2)
 
 	MOVB	0x1000000(R1), R2	// MOVB		16777216(R1), R2
 	MOVB	0x44332211(R1), R2	// MOVB		1144201745(R1), R2
@@ -643,6 +645,8 @@ TEXT	foo(SB), DUPOK|NOSPLIT, $-8
 	FMOVS	0x44332211(R1), F2	// FMOVS	1144201745(R1), F2
 	FMOVD	0x1000000(R1), F2	// FMOVD	16777216(R1), F2
 	FMOVD	0x44332211(R1), F2	// FMOVD	1144201745(R1), F2
+	FMOVQ	0x1000000(R1), F2	// FMOVQ	16777216(R1), F2
+	FMOVQ	0x44332211(R1), F2	// FMOVQ	1144201745(R1), F2
 
 // shifted or extended register offset.
 	MOVD	(R2)(R6.SXTW), R4               // 44c866f8

src/cmd/internal/obj/arm64/asm7.go

@@ -7276,6 +7276,8 @@ func (c *ctxt7) opldrr(p *obj.Prog, a obj.As, rt, rn, rm int16, extension bool)
 		op = OptionS<<10 | 0x3<<21 | 0x17<<27 | 1<<26
 	case AFMOVD:
 		op = OptionS<<10 | 0x3<<21 | 0x1f<<27 | 1<<26
+	case AFMOVQ:
+		op = OptionS<<10 | 0x7<<21 | 0x07<<27 | 1<<26
 	default:
 		c.ctxt.Diag("bad opldrr %v\n%v", a, p)
 		return 0
@@ -7308,6 +7310,8 @@ func (c *ctxt7) opstrr(p *obj.Prog, a obj.As, rt, rn, rm int16, extension bool)
 		op = OptionS<<10 | 0x1<<21 | 0x17<<27 | 1<<26
 	case AFMOVD:
 		op = OptionS<<10 | 0x1<<21 | 0x1f<<27 | 1<<26
+	case AFMOVQ:
+		op = OptionS<<10 | 0x5<<21 | 0x07<<27 | 1<<26
 	default:
 		c.ctxt.Diag("bad opstrr %v\n%v", a, p)
 		return 0