crypto: jitter - update implementation to 2.1.2

The Jitter RNG implementation is updated to comply with upstream version
2.1.2. The change covers the following aspects:

* Time variation measurement is conducted over the LFSR operation
instead of the XOR folding

* Invcation of stuck test during initialization

* Removal of the stirring functionality and the Von-Neumann
unbiaser as the LFSR using a primitive and irreducible polynomial
generates an identical distribution of random bits

This implementation was successfully used in FIPS 140-2 validations
as well as in German BSI evaluations.

This kernel implementation was tested as follows:

* The unchanged kernel code file jitterentropy.c is compiled as part
of user space application to generate raw unconditioned noise
data. That data is processed with the NIST SP800-90B non-IID test
tool to verify that the kernel code exhibits an equal amount of noise
as the upstream Jitter RNG version 2.1.2.

* Using AF_ALG with the libkcapi tool of kcapi-rng the Jitter RNG was
output tested with dieharder to verify that the output does not
exhibit statistical weaknesses. The following command was used:
kcapi-rng -n "jitterentropy_rng" -b 100000000000 | dieharder -a -g 200

* The unchanged kernel code file jitterentropy.c is compiled as part
of user space application to test the LFSR implementation. The
LFSR is injected a monotonically increasing counter as input and
the output is fed into dieharder to verify that the LFSR operation
does not exhibit statistical weaknesses.

* The patch was tested on the Muen separation kernel which returns
a more coarse time stamp to verify that the Jitter RNG does not cause
regressions with its initialization test considering that the Jitter
RNG depends on a high-resolution timer.

Tested-by: Reto Buerki <reet@codelabs.ch>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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