xwayland: import DMA-BUFs with GBM_BO_USE_RENDERING only (backport to server-1.20-branch)
Drop GBM_BO_USE_SCANOUT from the GBM_BO_IMPORT_FD import, add GBM_BO_USE_RENDERING to the GBM_BO_IMPORT_FD_MODIFIER import.
If the DMA-BUF cannot be scanned out, gbm_bo_import with GBM_BO_USE_SCANOUT will fail. However Xwayland doesn't need to scan-out the buffer and can work fine without scanout. Glamor only needs GBM_BO_USE_RENDERING.