glamor: Set RADEON_CREATE_PIXMAP_DRI2 for DRI3 pixmaps

Not doing this resulted in falling back to software for DRI3 client
presentation operations with ShadowPrimary.

(Ported from amdgpu commit 2989d40ef74d9966e8e8df2ef7727b2cc48d4960)
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>