brcmfmac: add dedicated debug level for firmware console logging

Both PCIe and SDIO devices have the possibility to log the firmware
console output in kernel log. For PCIe it is logged when PCIE debug
level is enabled. For SDIO it is logged when user specifies a non-zero
console interval through debugfs. This patch tries to make it a
bit more consistent. The firmware console output is only logged when
FWCON debug level is enabled.

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