brcmfmac: Unify methods to define and map firmware files.

All bus drivers (sdio, usb and pcie) require firmware files which
needs to be downloaded to the device, The definitions and mapping
of device id and revision to firmware and nvram file is done by
each bus driver. This patch creates common functions and defines
to simplify and unify the definition of these firmware and nvram
files and mapping.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>