hwrng: mxc-rnga - add driver support on boards with device tree

The driver works well on i.MX31 powered boards with device description
taken from board device tree, the only change to add to the driver is
the missing OF device id, the affected list of included headers and
indentation in platform driver struct are beautified a little.

Signed-off-by: Vladimir Zapolskiy <vz@mleia.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Kim Phillips <kim.phillips@arm.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>