cnss2: Collect device RAM dump during WLAN driver unload

There is a chance that firmware crashes while WLAN driver is
unloading. Collect device RAM dump for this case only in debug
builds in order to debug the issue. For other builds, ignore it
since device is going to be shutdown completely.

Change-Id: I16cab04744b376d3104f07255b4421d60ac22d20
Signed-off-by: Yue Ma <yuem@codeaurora.org>