Kernel: Add AnonymousVMObject constructor for a Vector of physical pages

This will be used later on by the AHCI code to create a Region
that spans over scattered DMA pages.

Kernel/VM/VMObject.h

@@ -88,6 +88,7 @@ public:
     }
 
 protected:
+    VMObject();
     explicit VMObject(size_t);
     explicit VMObject(const VMObject&);