file_sys: Cleanup to better match Switch file system constructs.

file_sys: Add factory class for RomFS file system.

src/core/file_sys/romfs_factory.h

@@ -0,0 +1,35 @@
+// Copyright 2018 yuzu emulator team
+// Licensed under GPLv2 or any later version
+// Refer to the license.txt file included.
+
+#pragma once
+
+#include <memory>
+#include <string>
+#include <vector>
+#include "common/common_types.h"
+#include "core/file_sys/filesystem.h"
+#include "core/hle/result.h"
+#include "core/loader/loader.h"
+
+namespace FileSys {
+
+/// File system interface to the RomFS archive
+class RomFS_Factory final : public FileSystemFactory {
+public:
+    explicit RomFS_Factory(Loader::AppLoader& app_loader);
+
+    std::string GetName() const override {
+        return "ArchiveFactory_RomFS";
+    }
+    ResultVal<std::unique_ptr<FileSystemBackend>> Open(const Path& path) override;
+    ResultCode Format(const Path& path, const FileSys::ArchiveFormatInfo& format_info) override;
+    ResultVal<ArchiveFormatInfo> GetFormatInfo(const Path& path) const override;
+
+private:
+    std::shared_ptr<FileUtil::IOFile> romfs_file;
+    u64 data_offset;
+    u64 data_size;
+};
+
+} // namespace FileSys