lib: Rename rsa-checksum.c to hash-checksum.c

rsa-checksum.c sontains the hash_calculate() implementations. Despite
the "rsa-" file prefix, this function is useful for other algorithms.

To prevent confusion, move this file to lib/, and rename it to
hash-checksum.c, to give it a more "generic" feel.

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/image-sig.c b/common/image-sig.c
index 4abd3c0..54f0eb2 100644
--- a/common/image-sig.c
+++ b/common/image-sig.c
@@ -17,7 +17,7 @@
 #endif /* !USE_HOSTCC*/
 #include <image.h>
 #include <u-boot/rsa.h>
-#include <u-boot/rsa-checksum.h>
+#include <u-boot/hash-checksum.h>
 
 #define IMAGE_MAX_HASHED_NODES		100