crypto: jitterentropy - replace long-held spinlock with mutex

In the Linux kernel, the following vulnerability has been resolved:

crypto: jitterentropy - replace long-held spinlock with mutex

jent_kcapi_random() serializes the shared jitterentropy state, but it

currently holds a spinlock across the jent_read_entropy() call. That

path performs expensive jitter collection and SHA3 conditioning, so

parallel readers can trigger stalls as contending waiters spin for

the same lock.

To prevent non-preemptible lock hold, replace rng->jent_lock with a

mutex so contended readers sleep instead of spinning on a shared lock

held across expensive entropy generation.