char: hw_random: convert drivers/char/hw_random/* to use module_platform_driver()

This patch converts the drivers in drivers/char/hw_random/* to use the
module_platform_driver() macro which makes the code smaller and a bit
simpler.

Cc: David S. Miller <davem@davemloft.net>
Cc: Josh Boyer <jwboyer@linux.vnet.ibm.com>
Cc: Matt Mackall <mpm@selenic.com>
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Jamie Iles <jamie@jamieiles.com>
Acked-by: Alexander Clouter <alex@digriz.org.uk>
Acked-by: Olof Johansson <olof@lixom.net>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>