Fix/Improve Hardware RNG for ODROID C1

[gparent]

Hello

From what I understand, by commiting efa186d which disables CONFIG_PM_RUNTIME, the init routines for the HW RNG are neither defined nor (obviously) automatically ran by the PM system and therefore entropy validation fails when rngd tries to use the device.

On a typical start up of rngd, this leads to the following series of messages , as seen on the forums, which understandably confuses poor user ctmme.

rngd 2-unofficial-mt.14 starting up...
block failed FIPS test: 0x17
block failed FIPS test: 0x17
block failed FIPS test: 0x17
Too many consecutive bad blocks of data, check entropy source!
Throttling down entropy source read speed...
block failed FIPS test: 0x17
block failed FIPS test: 0x17
block failed FIPS test: 0x17
block failed FIPS test: 0x17
block failed FIPS test: 0x17
block failed FIPS test: 0x17
block failed FIPS test: 0x17

Eventually it fails and rngd will bail out in the usual case.

My pull request is two-fold:

• It extracts the initialization/teardown code to separate functions matching the signature expected by struct hwrng callbacks, while keeping the power management code working the same way.
• It sets the initialization and cleanup callback of that struct so the code is called even when CONFIG_PM_RUNTIME is undefined. However I'm not sure the cleanup callback is needed here.

As this is my first kernel patch and I'm in no way familiar with the power management systems, please review thoroughly. In particular I wonder if assigning .cleanup is needed, and I'm not 100% sure the two calls that are added in the resume/suspend functions are side-effect free.

This fixes #157

[mdrjr]

Thank you so much for this one :)