brcm80211: fmac: add USB support for bcm43235/6/8 chipsets

This patch extends the use of the brcmfmac driver with support for
chipsets with a USB host interface. The first chipsets supported are
the bcm43235, bcm43236, and bcm43238 for which firmware has been
submitted.

This driver change has been successfully built for x86, x86_64,
ppc64, arm_le, and mips_be.

It has been tested successfully on x86 and x86_64.

Cc: M. Lambert <lambertm@westman.wave.ca>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Kan Yan <kanyan@broadcom.com>
Reviewed-by: Alwin Beukers <alwin@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>