Move spinlock to separate folder

kernel/spinlock/spinlock.c

@@ -0,0 +1,20 @@
+#include <stdatomic.h>
+#include <stdint.h>
+#include "spinlock.h"
+
+void spinlock_init(SpinLock *sl) {
+  atomic_store(&sl->lock, false);
+}
+
+void spinlock_acquire(SpinLock *sl) {
+  bool unlocked = false;
+  while (!atomic_compare_exchange_weak(&sl->lock, &unlocked, true)) {
+    unlocked = false;
+    SPINLOCK_HINT();
+  }
+}
+
+void spinlock_release(SpinLock *sl) {
+  atomic_store(&sl->lock, false);
+}
+