common/host_memory: Optimize for huge tables.

In theory, if we have 2 MB continously mapped, this should save one layer of TLB.
Let's make it at least more likely by aligning the memory.

src/common/host_memory.h

@@ -15,7 +15,7 @@ namespace Common {
  */
 class HostMemory {
 public:
-    explicit HostMemory(size_t backing_size, size_t virtual_size);
+    explicit HostMemory(size_t backing_size_, size_t virtual_size_);
     ~HostMemory();
 
     /**
@@ -52,11 +52,15 @@ public:
     }
 
 private:
+    size_t backing_size{};
+    size_t virtual_size{};
+
     // Low level handler for the platform dependent memory routines
     class Impl;
     std::unique_ptr<Impl> impl;
     u8* backing_base{};
     u8* virtual_base{};
+    size_t virtual_base_offset{};
 };
 
 } // namespace Common