drm/nouveau/pmu/gk208: implement gr power-up magic with gk110_pmu_pgob()

Before we moved gk110's implementation of this to pmu, the functions were
identical.  This commit just switches GK208 to use the new (more complete)
implementation of the power-up sequence.

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>