sdvx: option to disable Live2D (#777)

## Link to GitHub Issue or related Pull Request, if one exists
n/a

## Description of change
Adds an option to disable Live2D. Can be disabled everywhere, or just
during a song.

## Testing
Tested EG final and recent Nabla.

src/spice2x/launcher/options.h

@@ -97,6 +97,7 @@ namespace launcher {
             SDVXDigitalKnobSocd,
             spice2x_SDVXAsioDriver,
             SDVXAsioTwoChannel,
+            SDVXDisableLive2D,
             spice2x_SDVXSubPos,
             SDVXSubMonitorOverride,
             LoadDDRModule,