[video_core, hle] remove redundant parent references in system structs (#3908)

reworked a bit to remove references of parent objects and instead pass as arguments to methods to prevent useless reloads

Signed-off-by: lizzie <lizzie@eden-emu.dev>
Co-authored-by: maufeat <sahyno1996@gmail.com>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/3908
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Reviewed-by: crueter <crueter@eden-emu.dev>

src/core/core.h

@@ -438,7 +438,6 @@ public:
     /// Applies any changes to settings to this core instance.
     void ApplySettings();
 
-private:
     struct Impl;
     std::unique_ptr<Impl> impl;
 };