crypto: testmgr - Only disable migration in crypto_disable_simd_for_test()

crypto_disable_simd_for_test() disables preemption in order to receive a
stable per-CPU variable which it needs to modify in order to alter
crypto_simd_usable() results.

This can also be achived by migrate_disable() which forbidds CPU
migrations but allows the task to be preempted. The latter is important
for PREEMPT_RT since operation like skcipher_walk_first() may allocate
memory which must not happen with disabled preemption on PREEMPT_RT.

Use migrate_disable() in crypto_disable_simd_for_test() to achieve a
stable per-CPU pointer.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

crypto/testmgr.c

@@ -1061,14 +1061,14 @@ static void generate_random_testvec_config(struct testvec_config *cfg,
 
 static void crypto_disable_simd_for_test(void)
 {
-	preempt_disable();
+	migrate_disable();
 	__this_cpu_write(crypto_simd_disabled_for_test, true);
 }
 
 static void crypto_reenable_simd_for_test(void)
 {
 	__this_cpu_write(crypto_simd_disabled_for_test, false);
-	preempt_enable();
+	migrate_enable();
 }
 
 /*