This fixes 'update_flash' related problems.
update_flash needs to know in which platform is running so it can decide
whether to write clean-markers for JFFS2 images or not (for example in
FSL platforms).
https://jira.digi.com/browse/DEL-221 #resolve
https://jira.digi.com/browse/DEL-222 #resolve
Signed-off-by: Javier Viguera <javier.viguera@digi.com>