andr_image_data structure is used as a global representation of
boot image header structure. Introduce this new structure to
support all boot header versions : v0,v1.v2.v3.v4 and to support
v3 and v4 while maitaining support for v0,v1,v2.
The need of using andr_image_data comes from the change of header
structure in both version 3 and 4.
Rework android_image_get_kcomp() to support this new struct.