radeonsi: disable sdma for gfx10

Disable sdma on gfx10 until all timeouts bugs are fixed.

See:
    https://gitlab.freedesktop.org/mesa/mesa/issues/1907
    https://bugs.freedesktop.org/show_bug.cgi?id=111481



Reviewed-by: Marek Olšák <marek.olsak@amd.com>