sha1: add dedicated config option

The sha1 code is currently compiled for everyone, but in reality, it's
only used by the FIT code.  So make it optional just like MD5.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>

include/image.h

diff --git a/include/image.h b/include/image.h
index d2e78fe..dcf3a7b 100644
--- a/include/image.h
+++ b/include/image.h
@@ -56,6 +56,7 @@
 #include <libfdt.h>
 #include <fdt_support.h>
 #define CONFIG_MD5		/* FIT images need MD5 support */
+#define CONFIG_SHA1		/* and SHA1 */
 #endif
 
 /*

lib_generic/Makefile

diff --git a/lib_generic/Makefile b/lib_generic/Makefile
index c17179c..4b8ed3a 100644
--- a/lib_generic/Makefile
+++ b/lib_generic/Makefile
@@ -42,7 +42,7 @@
 COBJS-y += ldiv.o
 COBJS-$(CONFIG_MD5) += md5.o
 COBJS-y += net_utils.o
-COBJS-y += sha1.o
+COBJS-$(CONFIG_SHA1) += sha1.o
 COBJS-$(CONFIG_SHA256) += sha256.o
 COBJS-y += string.o
 COBJS-y	+= strmhz.o