The oversampling rate (OSR) value specifies the heuristically implied
entropy in the recorded data - H_submitter = 1/osr. A different entropy
estimate implies a different APT/RCT cutoff value. This change adds
support for OSRs 1 through 15. This OSR can be selected by the caller
of the Jitter RNG.

For this patch, the caller still uses one hard-coded OSR. A subsequent
patch allows this value to be configured.

In addition, the power-up self test is adjusted as follows:

* It allows the caller to provide an oversampling rate that should be
tested with - commonly it should be the same as used for the actual
runtime operation. This makes the power-up testing therefore consistent
with the runtime operation.

* It calls now jent_measure_jitter (i.e. collects the full entropy
that can possibly be harvested by the Jitter RNG) instead of only
jent_condition_data (which only returns the entropy harvested from
the conditioning component). This should now alleviate reports where
the Jitter RNG initialization thinks there is too little entropy.

* The power-up test now solely relies on the (enhanced) APT and RCT
test that is used as a health test at runtime.

The code allowing the different OSRs as well as the power-up test
changes are present in the user space version of the Jitter RNG 3.4.1
and thus was already in production use for some time.

Reported-by "Ospan, Abylay" <aospan@amazon.com>
Signed-off-by: Stephan Mueller <smueller@chronox.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>