hwrng: cavium - Check health status while reading random data

This RNG device is present on Marvell OcteonTx2 silicons as well and
also provides entropy health status.

HW continuously checks health condition of entropy and reports
faults. Fault is in terms of co-processor cycles since last fault
detected. This doesn't get cleared and only updated when new fault
is detected. Also there are chances of detecting false positives.
So to detect a entropy failure SW has to check if failures are
persistent ie cycles elapsed is frequently updated by HW.

This patch adds support to detect health failures using below algo.
1. Consider any fault detected before 10ms as a false positive and ignore.
10ms is chosen randomly, no significance.
2. Upon first failure detection make a note of cycles elapsed and when this
error happened in realtime (cntvct).
3. Upon subsequent failure, check if this is new or a old one by comparing
current cycles with the ones since last failure. cycles or time since
last failure is calculated using cycles and time info captured at (2).

HEALTH_CHECK status register is not available to VF, hence had to map
PF registers. Also since cycles are in terms of co-processor cycles,
had to retrieve co-processor clock rate from RST device.

Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: cavium - make two functions static

Functions cavium_rng_remove and cavium_rng_remove_vf are local to the
source and do not need to be in global scope, so make them static.

Cleans up sparse warnings:
drivers/char/hw_random/cavium-rng-vf.c:80:7: warning: symbol
'cavium_rng_remove_vf' was not declared. Should it be static?
drivers/char/hw_random/cavium-rng.c:65:7: warning: symbol
'cavium_rng_remove' was not declared. Should it be static?

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

hwrng: cavium - Add Cavium HWRNG driver for ThunderX SoC.

The Cavium ThunderX SoC has a hardware random number generator.
This driver provides support using the HWRNG framework.

Signed-off-by: Omer Khaliq <okhaliq@caviumnetworks.com>
Signed-off-by: Ananth Jasty <Ananth.Jasty@cavium.com>
Acked-by: David Daney <david.daney@cavium.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>