crypto: ofb - add output feedback mode

Add a generic version of output feedback mode. We already have support of
several hardware based transformations of this mode and the needed test
vectors but we somehow missed adding a generic software one. Fix this now.

Signed-off-by: Gilad Ben-Yossef <gilad@benyossef.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
diff --git a/crypto/Makefile b/crypto/Makefile
index ff5c2bbd..5c207c7 100644
--- a/crypto/Makefile
+++ b/crypto/Makefile
@@ -142,6 +142,7 @@
 obj-$(CONFIG_CRYPTO_USER_API_RNG) += algif_rng.o
 obj-$(CONFIG_CRYPTO_USER_API_AEAD) += algif_aead.o
 obj-$(CONFIG_CRYPTO_ZSTD) += zstd.o
+obj-$(CONFIG_CRYPTO_OFB) += ofb.o
 
 ecdh_generic-y := ecc.o
 ecdh_generic-y += ecdh.o