Add a basic kernel heap object.

Currently allocation always fails because we don't
have a way to allocate a physical page.

zion/CMakeLists.txt

@@ -5,6 +5,7 @@ add_executable(zion
   debug/debug.cpp
   interrupt/interrupt.cpp
   interrupt/interrupt_enter.s
+  memory/kernel_heap.cpp
   memory/paging_util.cpp
   zion.cpp)