kernel/process: Report total physical memory used to svcGetInfo

Reports the (mostly) correct size through svcGetInfo now for queries to
total used physical memory. This still doesn't correctly handle memory
allocated via svcMapPhysicalMemory, however, we don't currently handle
that case anyways.

src/core/hle/kernel/process.h

@@ -186,6 +186,9 @@ public:
         return random_entropy.at(index);
     }
 
+    /// Retrieves the total physical memory used by this process in bytes.
+    u64 GetTotalPhysicalMemoryUsed() const;
+
     /// Clears the signaled state of the process if and only if it's signaled.
     ///
     /// @pre The process must not be already terminated. If this is called on a