[arch][arm] add debug asserts to the non SMP spinlock routines

This should assert that the spinlock is not already held when acquiring
and vice-versa and that interrupts are disabled.

app/tests/thread_tests.c

@@ -558,12 +558,14 @@ static void spinlock_test(void) {
     printf("seems to work\n");
 
 #define COUNT (1024*1024)
+    arch_interrupt_save(&state, SPIN_LOCK_FLAG_INTERRUPTS);
     uint32_t c = arch_cycle_count();
     for (uint i = 0; i < COUNT; i++) {
         spin_lock(&lock);
         spin_unlock(&lock);
     }
     c = arch_cycle_count() - c;
+    arch_interrupt_restore(state, SPIN_LOCK_FLAG_INTERRUPTS);
 
     printf("%u cycles to acquire/release lock %u times (%u cycles per)\n", c, COUNT, c / COUNT);