Finish address_manager to vm_space transition

src/include/kernel_memory.h

@@ -25,6 +25,9 @@ namespace memory {
 	/// Max size of the kernel heap
 	static const size_t kernel_max_heap = 0x800000000; // 32GiB
 
+	/// Start of the kernel heap
+	static const uintptr_t heap_start = page_offset - kernel_max_heap;
+
 	/// Helper to determine if a physical address can be accessed
 	/// through the page_offset area.
 	inline bool page_mappable(uintptr_t a) { return (a & page_offset) == 0; }