crypto: jitter - reuse allocated entropy collector

In case a health test error occurs during runtime, the power-up health
tests are rerun to verify that the noise source is still good and
that the reported health test error was an outlier. For performing this
power-up health test, the already existing entropy collector instance
is used instead of allocating a new one. This change has the following
implications:

* The noise that is collected as part of the newly run health tests is
  inserted into the entropy collector and thus stirs the existing
  data present in there further. Thus, the entropy collected during
  the health test is not wasted. This is also allowed by SP800-90B.

* The power-on health test is not affected by the state of the entropy
  collector, because it resets the APT / RCT state. The remainder of
  the state is unrelated to the health test as it is only applied to
  newly obtained time stamps.

This change also fixes a bug report about an allocation while in an
atomic lock (the lock is taken in jent_kcapi_random, jent_read_entropy
is called and this can call jent_entropy_init).

Fixes: 04597c8d

 ("jitter - add RCT/APT support for different OSRs")
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>