brcmfmac: Adding msgbuf protocol.

This patch will add the msgbuf protocol. This protocol is used by
the soon to be added new bus interface PCIe. Msgbuf is a protocol
where most data is and remains located on the host (driver) side
and transferred by DMA from and to device. Msgbuf is the protocol
which takes care of the signalling of the buffers between host and
device which identifies this DMA-able data.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Daniel (Deognyoun) Kim <dekim@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>