add SHA256 support

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Francesco Albanese <Francesco.Albanese@swisscom.com>
diff --git a/lib_generic/Makefile b/lib_generic/Makefile
index dca3a6c..4f6ce73 100644
--- a/lib_generic/Makefile
+++ b/lib_generic/Makefile
@@ -38,6 +38,7 @@
 COBJS-y += ldiv.o
 COBJS-$(CONFIG_MD5) += md5.o
 COBJS-y += sha1.o
+COBJS-$(CONFIG_SHA256) += sha256.o
 COBJS-y += string.o
 COBJS-y += vsprintf.o
 COBJS-y += zlib.o