include/image.h: sparse fixes

include/image.h:378:1: warning: cast to restricted __be32
include/image.h:381:1: warning: cast to restricted __be32
include/image.h:382:1: warning: cast to restricted __be32
include/image.h:383:1: warning: cast to restricted __be32

fix by annotating image header integers big endian.

Signed-off-by: Kim Phillips <kim.phillips@freescale.com>