drm/nouveau/bios/init: handle INIT_RESET_BEGUN devinit opcode

Signal that the reset sequence has begun.

This opcode signals that the software reset sequence has begun.
Ordinarily, no actual operations are performed by the opcode.
However it allows for possible software work arounds by devinit
engines in software agents other than the VBIOS, such as the resman,
FCODE, and EFI driver.

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Reviewed-by: Lyude Paul <lyude@redhat.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>