Made some changes from review comments:

- Made LoadKernelSystemMode return a pair consisting of a system mode and a result code (Could use review).
- Deleted ErrorOpenGL error code in favor of just having ErrorVideoCore.
- Made dialog messages more clear.
- Compared archive ID in fs_user.cpp to ArchiveIdCode::NCCH as opposed to hex magic.
- Cleaned up some other stuff.

src/core/file_sys/archive_ncch.cpp

@@ -37,7 +37,8 @@ ResultVal<std::unique_ptr<ArchiveBackend>> ArchiveFactory_NCCH::Open(const Path&
     auto file = std::make_shared<FileUtil::IOFile>(file_path, "rb");
 
     if (!file->IsOpen()) {
-        return ResultCode(-1); // TODO(Subv): Find the right error code
+        return ResultCode(ErrorDescription::FS_NotFound, ErrorModule::FS, ErrorSummary::NotFound,
+                          ErrorLevel::Status);
     }
     auto size = file->GetSize();