cbfstool: Deserialize CBFS master header when reading image

Rather than  using [hn]to[nh] whenever accessing a member of the CBFS
header, deserialize the header when opening the CBFS image. The header
is no longer a pointer inside the CBFS buffer, but a separate struct,
a copy of the original header in a host-friendly format. This kills
more of the ntohl usage.

Change-Id: I5f8a5818b9d5a2d1152b1906249c4a5847d02bac
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/5121
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Ronald G. Minnich <rminnich@gmail.com>

util/cbfstool/cbfs_image.h

@@ -34,6 +34,8 @@ struct cbfs_image {
 /* Given a pointer, serialize the header from host-native byte format
  * to cbfs format, i.e. big-endian. */
 void cbfs_put_header(void *dest, const struct cbfs_header *header);
+/* Or deserialize into host-native format */
+void cbfs_get_header(struct cbfs_header *header, const void *src);
 
 /* Creates an empty CBFS image by given size, and description to its content
  * (bootblock, align, header location, starting offset of CBFS entries.