[Zion] Introduce the Kernel VMM to centralize allocs.

zion/memory/kernel_vmm.h

@@ -0,0 +1,17 @@
+#pragma once
+
+#include <stdint.h>
+
+#include "memory/constants.h"
+
+class KernelVmm {
+ public:
+  KernelVmm();
+
+  static uint64_t AcquireSlabHeapRegion(uint64_t slab_size_bytes);
+
+ private:
+  uint64_t next_slab_heap_page_ = kKernelSlabHeapStart;
+
+  uint64_t AcquireSlabHeapRegionInternal(uint64_t slab_size_bytes);
+};