brcmfmac: introduce tracepoints for message logging

Inspired by tracing functionality added by Seth Forshee in the
brcmsmac driver, this patch adds similar functionality to brcmfmac.

Reviewed-by: Piotr Haber <phaber@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>