brcmsmac: Add support for writing debug messages to the trace buffer

Add a new brcmsmac_msg trace system to enable writing of debug messages
to the trace buffer, and add brcms_* macros for storing device debug
messages in the trace buffer in addition to the printk log buffer.

Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Arend van Spriel <arend@broadcom.com>
Tested-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>