hwrng: bcm63xx - allow building for BMIPS_GENERIC

Now that we have device tree support and BCM6368 is supported in BMIPS_GENERIC,
we can use it for BMIPS_GENERIC too.

Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>