fix gamescope for older GPUs

[korewaChino]

This PR patches the terra-gamescope package so that by default the SDL backend will be selected regardless of Wayland display support or not, requiring users to explicitly set --backend=wayland if they want to use the new Wayland backend for Gamescope, at the detriment of newer GPUs that support the Vulkan DRM modifiers feature.

Should work regardless on those aforementioned GPUs however.

Patch to work around https://github.com/ValveSoftware/gamescope/issues/1218 on older GPUs.

If this patch works we may be able to simply obsolete gamescope-legacy