[new uImage] Move CHUNKSZ definition to image.h

CHUNKSZ defined for PPC and M68K is set to the same value of 64K,
move this definition to a common header.

Signed-off-by: Marian Balakowicz <m8@semihalf.com>
diff --git a/include/image.h b/include/image.h
index c9f4298..aab3f44 100644
--- a/include/image.h
+++ b/include/image.h
@@ -164,6 +164,13 @@
 	uint8_t		ih_name[IH_NMLEN];	/* Image Name		*/
 } image_header_t;
 
+/*
+ * Some systems (for example LWMON) have very short watchdog periods;
+ * we must make sure to split long operations like memmove() or
+ * crc32() into reasonable chunks.
+ */
+#define CHUNKSZ (64 * 1024)
+
 #define image_to_cpu(x)		ntohl(x)
 #define cpu_to_image(x)		htonl(x)