drm/nouveau: restore performance mode a bit later.

Otherwice code that responsible for idling the card can't work.
BIOS init tables are supposed to init the clocks to correct values,
so that shouldn't cause any problems (we don't reclock by default anyway)

Signed-off-by: Maxim Levitsky <maximlevitsky@gmail.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>