hwrng: rockchip - add support for RK3576's RNG

hwrng: rockchip - add support for RK3576's RNG

The Rockchip RK3576 SoC uses a new hardware random number generator IP.
It's also used on the Rockchip RK3562 and the Rockchip RK3528.

It has several modes of operation and self-checking features that are
not implemented here. For starters, it has a DRNG output, which is an
AES-CTR pseudo-random number generator that can be reseeded from the
true entropy regularly.

However, it also allows for access of the true entropy generator
directly. This entropy is generated from an oscillator.

There are several configuration registers which we don't touch here. The
oscillator can be switched between a "CRO" and "STR" oscillator, and the
length of the oscillator can be configured.

The hardware also supports some automatic continuous entropy quality
checking, which is also not implemented in this driver for the time
being.

The output as-is has been deemed sufficient to be useful:

  rngtest: starting FIPS tests...
  rngtest: bits received from input: 20000032
  rngtest: FIPS 140-2 successes: 997
  rngtest: FIPS 140-2 failures: 3
  rngtest: FIPS 140-2(2001-10-10) Monobit: 0
  rngtest: FIPS 140-2(2001-10-10) Poker: 1
  rngtest: FIPS 140-2(2001-10-10) Runs: 1
  rngtest: FIPS 140-2(2001-10-10) Long run: 1
  rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
  rngtest: input channel speed: (min=17.050; avg=1897.272;
           max=19531250.000)Kibits/s
  rngtest: FIPS tests speed: (min=44.773; avg=71.179; max=96.820)Mibits/s
  rngtest: Program run time: 11760715 microseconds
  rngtest: bits received from input: 40000032
  rngtest: FIPS 140-2 successes: 1997
  rngtest: FIPS 140-2 failures: 3
  rngtest: FIPS 140-2(2001-10-10) Monobit: 0
  rngtest: FIPS 140-2(2001-10-10) Poker: 1
  rngtest: FIPS 140-2(2001-10-10) Runs: 1
  rngtest: FIPS 140-2(2001-10-10) Long run: 1
  rngtest: FIPS 140-2(2001-10-10) Continuous run: 0
  rngtest: input channel speed: (min=17.050; avg=1798.618;
           max=19531250.000)Kibits/s
  rngtest: FIPS tests speed: (min=44.773; avg=64.561; max=96.820)Mibits/s
  rngtest: Program run time: 23507723 microseconds

Stretching the entropy can then be left up to Linux's actual entropy
pool.

Signed-off-by: Nicolas Frattaroli <nicolas.frattaroli@collabora.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>