brcmfmac: enable firmware console logging functionality

Address of rte console was not initialized and so console logging
functionality didn't kick in. This patch fixes it and makes console
polling interval a debugfs variable.

Reviewed-by: Franky Lin <frankyl@broadcom.com>
Signed-off-by: Daniel Kim <dekim@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>