hwrng: bcm63xx - Remove since bcm2835-rng takes over

bcm2835-rng is now capable of supporting the BCM63xx hardware, so remove
the driver which duplicates the same functionality.

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>