aes/asm/bsaes-armv7: fix kernel-side XTS and harmonize with Linux.

XTS bug spotted and fix suggested by Adrian Kotelba.

(Imported from upstream's e620e5ae37bc3fc5e457ebf3edcdd01b20f8c5dd.)

Another patch we missed.

Change-Id: Ibea40eeec01a49b29064b14631706756795c9592
Reviewed-on: https://boringssl-review.googlesource.com/4489
Reviewed-by: Adam Langley <agl@google.com>

crypto/aes/asm/bsaes-armv7.pl

@@ -703,7 +703,7 @@ $code.=<<___;
 # define BSAES_ASM_EXTENDED_KEY
 # define XTS_CHAIN_TWEAK
 # define __ARM_ARCH__ __LINUX_ARM_ARCH__
-# define __ARM_MAX_ARCH__ __LINUX_ARM_ARCH__
+# define __ARM_MAX_ARCH__ 7
 #endif
 
 #ifdef __thumb__
@@ -2087,9 +2087,11 @@ bsaes_xts_decrypt:
 	vld1.8	{@XMM[8]}, [r0]			@ initial tweak
 	adr	$magic, .Lxts_magic
 
+#ifndef	XTS_CHAIN_TWEAK
 	tst	$len, #0xf			@ if not multiple of 16
 	it	ne				@ Thumb2 thing, sanity check in ARM
 	subne	$len, #0x10			@ subtract another 16 bytes
+#endif
 	subs	$len, #0x80
 
 	blo	.Lxts_dec_short