Add runtime power management to the imx-rngc driver. Disable the peripheral clock when the rngc is idle. The callback functions from struct hwrng wake the rngc up when they're called and set it to idle on exit. Helper functions which are invoked from the callbacks assume that the rngc is active. Device init and probe are done before runtime pm is enabled. The peripheral clock will be handled manually during these steps. Do not use devres any more to enable/disable the peripheral clock, this conflicts with runtime pm. Signed-off-by: Martin Kaiser <martin@kaiser.cx> Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>