Kernel: Make PhysicalZone an eternally allocated object

Until we start supporting hot-pluggable RAM, these will not be freed
or reallocated during the kernel's lifetime. :^)

Kernel/VM/PhysicalZone.h

@@ -19,6 +19,7 @@ namespace Kernel {
 // The allocator uses a buddy block scheme internally.
 
 class PhysicalZone {
+    AK_MAKE_ETERNAL
 public:
     static constexpr size_t ZONE_CHUNK_SIZE = PAGE_SIZE / 2;
     using ChunkIndex = i16;