crypto: ixp4xx - Select CRYPTO_AUTHENC

Without CRYPTO_AUTHENC the driver fails to build:
drivers/built-in.o: In function `ixp_module_init':
ixp4xx_crypto.c:(.init.text+0x3250): undefined reference to `crypto_aead_type'
Signed-off-by: NImre Kaloz <kaloz@openwrt.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/Kconfig

@@ -195,6 +195,7 @@ config CRYPTO_DEV_IXP4XX
 	depends on ARCH_IXP4XX
 	select CRYPTO_DES
 	select CRYPTO_ALGAPI
+	select CRYPTO_AUTHENC
 	select CRYPTO_BLKCIPHER
 	help
 	  Driver for the IXP4xx NPE crypto engine.