kselftest/arm64: Always encourage preemption for za-test

Since we now have an explicit test for the syscall ABI there is no need for
za-test to cover getpid() so just unconditionally do sched_yield() like we
do in fpsimd-test.
Signed-off-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20220829154452.824870-2-broonie@kernel.orgSigned-off-by: Catalin Marinas <catalin.marinas@arm.com>

tools/testing/selftests/arm64/fp/za-test.S

@@ -287,12 +287,7 @@ _start:
 	subs	x21, x21, #1
 	b.ne	0b
 
-	and	x8, x22, #127		// Every 128 interations...
-	cbz	x8, 0f
-	mov	x8, #__NR_getpid	// (otherwise minimal syscall)
-	b	1f
-0:
-	mov	x8, #__NR_sched_yield	// ...encourage preemption
+	mov	x8, #__NR_sched_yield	// encourage preemption
 1:
 	svc	#0