[CRYPTO] salsa20: Add x86-64 assembly version

This is the x86-64 version of the Salsa20 stream cipher algorithm. The
original assembly code came from
<http://cr.yp.to/snuffle/salsa20/amd64-3/salsa20.s>. It has been
reformatted for clarity.

Signed-off-by: Tan Swee Heng <thesweeheng@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/Kconfig b/crypto/Kconfig
index 221356b..b0481f7 100644
--- a/crypto/Kconfig
+++ b/crypto/Kconfig
@@ -504,6 +504,21 @@
 	  The Salsa20 stream cipher algorithm is designed by Daniel J.
 	  Bernstein <djb@cr.yp.to>. See <http://cr.yp.to/snuffle.html>
 
+config CRYPTO_SALSA20_X86_64
+	tristate "Salsa20 stream cipher algorithm (x86_64) (EXPERIMENTAL)"
+	depends on (X86 || UML_X86) && 64BIT
+	depends on EXPERIMENTAL
+	select CRYPTO_BLKCIPHER
+	select CRYPTO_SALSA20
+	help
+	  Salsa20 stream cipher algorithm.
+
+	  Salsa20 is a stream cipher submitted to eSTREAM, the ECRYPT
+	  Stream Cipher Project. See <http://www.ecrypt.eu.org/stream/>
+
+	  The Salsa20 stream cipher algorithm is designed by Daniel J.
+	  Bernstein <djb@cr.yp.to>. See <http://cr.yp.to/snuffle.html>
+
 config CRYPTO_DEFLATE
 	tristate "Deflate compression algorithm"
 	select CRYPTO_ALGAPI