hwrng: iproc-rng200 - Implement suspend and resume calls

[ Upstream commit 8e03dd62e5be811efbf0cbeba47e79e793519105 ]

Chips such as BCM7278 support system wide suspend/resume which will
cause the HWRNG block to lose its state and reset to its power on reset
register values. We need to cleanup and re-initialize the HWRNG for it
to be functional coming out of a system suspend cycle.

Fixes: c3577f61 ("hwrng: iproc-rng200 - Add support for BCM7278")
Signed-off-by: Florian Fainelli <florian.fainelli@broadcom.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Sasha Levin <sashal@kernel.org>