BIOS scripts usually make an attempt to reset the AGP controller,
however on some nv4x cards doing it properly involves switching FW off
and on: if we do that without updating the AGP bridge settings
accordingly (e.g. with the corresponding calls to agp_enable()) we
will be locking ourselves out of the card MMIO space. Do it from
nouveau_mem_reset_agp() before the init scripts are executed.

Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>