crypto: jitter - set default OSR to 3

The user space Jitter RNG library uses the oversampling rate of 3 which
implies that each time stamp is credited with 1/3 bit of entropy. To
obtain 256 bits of entropy, 768 time stamps need to be sampled. The
increase in OSR is applied based on a report where the Jitter RNG is
used on a system exhibiting a challenging environment to collect
entropy.

This OSR default value is now applied to the Linux kernel version of
the Jitter RNG as well.

The increase in the OSR from 1 to 3 also implies that the Jitter RNG is
now slower by default.
Reported-by: Jeff Barnes <jeffbarnes@microsoft.com>
Signed-off-by: Stephan Mueller <smueller@chronox.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/Kconfig

@@ -1305,7 +1305,7 @@ config CRYPTO_JITTERENTROPY_MEMORY_BLOCKSIZE
 config CRYPTO_JITTERENTROPY_OSR
 	int "CPU Jitter RNG Oversampling Rate"
 	range 1 15
-	default 1
+	default 3
 	help
 	  The Jitter RNG allows the specification of an oversampling rate (OSR).
 	  The Jitter RNG operation requires a fixed amount of timing