Kernel: Change kmalloc lock to be recursive

If the heap code dumps a stack trace (e.g. out of memory) then
it may recursively call into it. Rather than deadlocking, allow
recursion.

Kernel/Heap/kmalloc.cpp

@@ -67,7 +67,7 @@ bool g_dump_kmalloc_stacks;
 static u8* s_next_eternal_ptr;
 static u8* s_end_of_eternal_range;
 
-static SpinLock s_lock;
+static RecursiveSpinLock s_lock; // needs to be recursive because of dump_backtrace()
 
 void kmalloc_init()
 {

Kernel/SpinLock.h

@@ -103,6 +103,11 @@ public:
     {
         return m_lock.load(AK::memory_order_consume) != 0;
     }
+
+    ALWAYS_INLINE void initialize()
+    {
+        m_lock.store(0, AK::memory_order_release);
+    }
 };
 
 template <typename BaseType = u32, typename LockType = SpinLock<BaseType>>