iwlwifi: mvm: allow firmware crashes to wake system for debug

When the D3 firmware crashes, it can be helpful for debugging to
resume the system to get the SRAM snapshot to see why it crashed.
Allow enabling this with a debugfs option.

Reviewed-by: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Signed-off-by: Johannes Berg <johannes.berg@intel.com>