give rdrand some credit

try to credit rdrand/rdseed with some entropy

In VMs but even modern hardware, we're super starved for entropy, and
while we can and do wear a tin foil hat, it's very hard to argue that
rdrand and rdtsc add zero enttropy.

drivers/char/random.c

@@ -1768,6 +1768,8 @@ static void __init init_std_data(struct entropy_store *r)
 		if (!arch_get_random_seed_long(&rv) &&
 		    !arch_get_random_long(&rv))
 			rv = random_get_entropy();
+		else
+			credit_entropy_bits(r, 1);
 		mix_pool_bytes(r, &rv, sizeof(rv));
 	}
 	mix_pool_bytes(r, utsname(), sizeof(*(utsname())));