crypto/internal/fips140/aes: actually use the VTBL instruction on arm64

Support for the VTBL instruction was added in CL 110015 - use it
directly, rather than using WORD encodings. Note that one of the
WORD encodings does not actually match the instruction in the
comment - use the instruction that matches the existing encoding
instead.

Change-Id: I1933162f8144a6b86b38e8b550d36907131b1dd4
Reviewed-on: https://go-review.googlesource.com/c/go/+/666795
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: David Chase <drchase@google.com>
Reviewed-by: Filippo Valsorda <filippo@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>

Author: 4a6f656c

src/crypto/internal/fips140/aes/aes_arm64.s

@@ -134,7 +134,7 @@ TEXT ·expandKeyAsm(SB),NOSPLIT,$0
 	MOVW	$0x1b, R14
 ks128Loop:
 		VMOV	R7, V2.S[0]
-		WORD	$0x4E030042       // TBL V3.B16, [V2.B16], V2.B16
+		VTBL	V3.B16, [V2.B16], V2.B16
 		AESE	V0.B16, V2.B16    // Use AES to compute the SBOX
 		EORW	R13, R4
 		LSLW	$1, R13           // Compute next Rcon
@@ -180,7 +180,7 @@ ks192:
 ks192Loop:
 		STPW.P	(R6, R7), 8(R10)
 		VMOV	R7, V2.S[0]
-		WORD	$0x4E030042 //TBL	V3.B16, [V2.B16], V2.B16
+		VTBL	V3.B16, [V2.B16], V2.B16
 		AESE	V0.B16, V2.B16
 		EORW	R13, R2
 		LSLW	$1, R13
@@ -233,7 +233,7 @@ ks256Loop:
 		STPW.P	(R4, R5), 8(R10)
 		STPW.P	(R6, R7), 8(R10)
 		VMOV	R7, V2.S[0]
-		WORD	$0x4E030042 //TBL	V3.B16, [V2.B16], V2.B16
+		VTBL	V3.B16, [V2.B16], V2.B16
 		AESE	V0.B16, V2.B16
 		EORW	R13, R0
 		LSLW	$1, R13
@@ -244,7 +244,7 @@ ks256Loop:
 		EORW	R1, R2
 		EORW	R2, R3
 		VMOV	R3, V2.S[0]
-		WORD	$0x4E040042 //TBL	V3.B16, [V2.B16], V2.B16
+		VTBL	V4.B16, [V2.B16], V2.B16
 		AESE	V0.B16, V2.B16
 		VMOV	V2.S[0], R9
 		EORW	R9, R4