With the Cygnus port, we needed to add at least "|| ARCH_BCM_CYGNUS"
to let the module get built on a cygnus-only kernel. However, I
anticipate having a port for Kona soon, so just present the module on
all of BCM.
v2: Keep allowing selection with ARCH_BCM2835, since ARCH_BCM doesn't
exist on arm64.