brcmfmac: conditionally compile firmware protocol source code

brcmfmac: conditionally compile firmware protocol source code

The host-interface can select which protocol implementation it
needs. Selecting PCIe will include the msgbuf protocol and selecting
USB and/or SDIO will include the bcdc protocol. The PCIe kconfig
option assures the dependencies for msgbuf are met, ie. HAS_DMA.

Reported-by: Geert Uytterhoeven <[email protected]>
Reviewed-by: Franky (Zhenhui) Lin <[email protected]>
Reviewed-by: Hante Meuleman <[email protected]>
Reviewed-by: Daniel (Deognyoun) Kim <[email protected]>
Reviewed-by: Pieter-Paul Giesberts <[email protected]>
Signed-off-by: Arend van Spriel <[email protected]>
Signed-off-by: John W. Linville <[email protected]>