drm/nouveau: drop DRIVER_PCI_DMA and DRIVER_SG

The former doesn't do anything without DRIVER_HAVE_DMA (which is
force-disabled for kms drivers anyway). The latter isn't used by the
(kms) nouveau ddx.

Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@gmail.com>