brcmfmac: expose device memory to devcoredump subsystem

Upon PSM watchdog event received from firmware the driver will obtain
a memory snapshot of the device and expose it to user-space through
the devcoredump framework. This will trigger a uevent.

Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>