secimage: Use libz's crc32 function

This is to trick libreboot into not deleting misc.c when checking
out coreboot.

Change-Id: I8f0bb5cb3eb5681f99c616ae03de126efab852a9
Signed-off-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-on: http://review.coreboot.org/11134
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/broadcom/secimage/Makefile.inc

@@ -4,7 +4,7 @@ secimageobj += io.o
 secimageobj += misc.o
 secimageobj += sbi.o
 
-LIBS = -lssl -lcrypto
+LIBS = -lssl -lcrypto -lz
 
 additional-dirs += $(objutil)/broadcom/secimage