crypto: remove hand encoded amd64 instructions

Replace BYTE.. encodings with asm. This is possible due to asm
implementing more instructions and removal of
MOV $0, reg -> XOR reg, reg transformation from asm.

Change-Id: I011749ab6b3f64403ab6e746f3760c5841548b57
Reviewed-on: https://go-review.googlesource.com/97936
Run-TryBot: Ilya Tocar <ilya.tocar@intel.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/crypto/elliptic/p256_asm_amd64.s

@@ -1486,7 +1486,7 @@ TEXT p256MulInternal(SB),NOSPLIT,$0
 	ADCQ mul0, acc2
 	ADCQ $0, mul1
 	MOVQ mul1, acc3
-	BYTE $0x48; BYTE $0xc7; BYTE $0xc5; BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00   // MOVQ $0, BP
+	MOVQ $0, BP
 	// Add bits [511:256] of the result
 	ADCQ acc0, acc4
 	ADCQ acc1, acc5
@@ -1628,7 +1628,7 @@ TEXT p256SqrInternal(SB),NOSPLIT,$0
 	ADCQ mul0, acc2
 	ADCQ $0, mul1
 	MOVQ mul1, acc3
-	BYTE $0x48; BYTE $0xc7; BYTE $0xc5; BYTE $0x00; BYTE $0x00; BYTE $0x00; BYTE $0x00   // MOVQ $0, BP
+	MOVQ $0, BP
 	// Add bits [511:256] of the result
 	ADCQ acc0, t0
 	ADCQ acc1, t1

src/hash/crc32/crc32_amd64.s

@@ -37,8 +37,7 @@ align_2:
 	BTQ $1, BX
 	JNC align_4
 
-	// CRC32W (SI), AX
-	BYTE $0x66; BYTE $0xf2; BYTE $0x0f; BYTE $0x38; BYTE $0xf1; BYTE $0x06
+	CRC32W (SI), AX
 
 	SUBQ $2, CX
 	ADDQ $2, SI
@@ -47,8 +46,7 @@ align_4:
 	BTQ $2, BX
 	JNC aligned
 
-	// CRC32L (SI), AX
-	BYTE $0xf2; BYTE $0x0f; BYTE $0x38; BYTE $0xf1; BYTE $0x06
+	CRC32L (SI), AX
 
 	SUBQ $4, CX
 	ADDQ $4, SI
@@ -68,16 +66,14 @@ less_than_8:
 	BTQ $2, CX
 	JNC less_than_4
 
-	// CRC32L (SI), AX
-	BYTE $0xf2; BYTE $0x0f; BYTE $0x38; BYTE $0xf1; BYTE $0x06
+	CRC32L (SI), AX
 	ADDQ $4, SI
 
 less_than_4:
 	BTQ $1, CX
 	JNC less_than_2
 
-	// CRC32W (SI), AX
-	BYTE $0x66; BYTE $0xf2; BYTE $0x0f; BYTE $0x38; BYTE $0xf1; BYTE $0x06
+	CRC32W (SI), AX
 	ADDQ $2, SI
 
 less_than_2: