hwrng: bcm2835 - Add Broadcom BCM2835 RNG driver

This adds a driver for random number generator present on Broadcom BCM2835 SoC,
used in Raspberry Pi and Roku 2 devices.

Signed-off-by: Dom Cobley <popcornmix@gmail.com>
Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Tested-by: Stephen Warren <swarren@wwwdotorg.org>
Cc: Herbert Xu <herbert@gondor.apana.org.au>
Cc: Stephen Warren <swarren@wwwdotorg.org>
Cc: Matt Mackall <mpm@selenic.com>
Cc: linux-rpi-kernel@lists.infradead.org
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>