Adding the ddb size into the devide info will avoid
platform checks while computing wm.

v2: Added comment and WARN_ON if ddb size is zero.(Jani)
v3: Added WARN_ON at the right place.(Jani)
Suggested-by: NAnder Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: NDeepak M <m.deepak@intel.com>
Signed-off-by: NJani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1473931870-7724-1-git-send-email-m.deepak@intel.com