brcmfmac: print firmware messages after a firmware crash

Normally firmware messages are printed with debugging enabled only. It's
a good idea as firmware may print a lot of messages that normal users
don't need to care about.

However, on firmware crash, it may be very helpful to log all recent
messages. There is almost always a backtrace available as well as rought
info on the latest actions/state.

Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Reviewed-by: Arend van Spriel <arend.vanspriel@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>