crypto: arm/chacha20 - always use vrev for 16-bit rotates

The 4-way ChaCha20 NEON code implements 16-bit rotates with vrev32.16,
but the one-way code (used on remainder blocks) implements it with
vshl + vsri, which is slower.  Switch the one-way code to vrev32.16 too.
Signed-off-by: NEric Biggers <ebiggers@google.com>
Acked-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/arm/crypto/chacha20-neon-core.S

@@ -51,9 +51,8 @@ ENTRY(chacha20_block_xor_neon)
 .Ldoubleround:
 	// x0 += x1, x3 = rotl32(x3 ^ x0, 16)
 	vadd.i32	q0, q0, q1
-	veor		q4, q3, q0
-	vshl.u32	q3, q4, #16
-	vsri.u32	q3, q4, #16
+	veor		q3, q3, q0
+	vrev32.16	q3, q3
 
 	// x2 += x3, x1 = rotl32(x1 ^ x2, 12)
 	vadd.i32	q2, q2, q3
@@ -82,9 +81,8 @@ ENTRY(chacha20_block_xor_neon)
 
 	// x0 += x1, x3 = rotl32(x3 ^ x0, 16)
 	vadd.i32	q0, q0, q1
-	veor		q4, q3, q0
-	vshl.u32	q3, q4, #16
-	vsri.u32	q3, q4, #16
+	veor		q3, q3, q0
+	vrev32.16	q3, q3
 
 	// x2 += x3, x1 = rotl32(x1 ^ x2, 12)
 	vadd.i32	q2, q2, q3