[kutil] Protect heap allocation with a spinlock

Don't allow multiple cores to access the heap datastructures at once.

src/libraries/kutil/heap_allocator.cpp

@@ -89,6 +89,8 @@ heap_allocator::allocate(size_t length)
 	if (order > max_order)
 		return nullptr;
 
+	scoped_lock lock {m_lock};
+
 	mem_header *header = pop_free(order);
 	header->set_used(true);
 	m_allocated_size += (1 << order);
@@ -104,6 +106,8 @@ heap_allocator::free(void *p)
 	kassert(addr >= m_start && addr < m_end,
 		"Attempt to free non-heap pointer");
 
+	scoped_lock lock {m_lock};
+
 	mem_header *header = reinterpret_cast<mem_header *>(p);
 	header -= 1; // p points after the header
 	header->set_used(false);

src/libraries/kutil/include/kutil/heap_allocator.h

@@ -3,6 +3,7 @@
 /// A buddy allocator for a memory heap
 
 #include <stddef.h>
+#include "kutil/spinlock.h"
 
 namespace kutil {
 
@@ -57,6 +58,8 @@ protected:
 	mem_header *m_free[max_order - min_order + 1];
 	size_t m_allocated_size;
 
+	spinlock m_lock;
+
 	heap_allocator(const heap_allocator &) = delete;
 };