brcmfmac: introduce module parameter to force successful probe

The module parameter can be used to ensure the probe succeeds thus
claiming the device and allowing post-mortem debugging in case of
firmware crash. It is only available when select CONFIG_BRCMDBG.

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>