Until now, the v0 image creation function was expecting the
configuration parameters to be ordered with first the configuration
parameters affecting the main header, then the DATA configuration
parameters that affect the extended header, then the payload.

However, with the recently added ability to override the destination
address or execution address, the configuration options corresponding
to those values may now appear at the end of the configuration
options. This commit allows to handle that by making the image
creation more flexible:

 - The configuration options for the main header are just searched
   amongst all options, the first match is used.

 - When building the extension header with the DATA options, all DATA
   options from the configuration file are used, in the order in which
   they appear in the kwbimage.cfg file.

This will for example allow a kwbimage.cfg for a v0 image to not
specify any destination or execution address, and simply override it
from the command line.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Tested-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>