drm/nouveau/gpio: check the gpio function 16 in the power check as well

Added GPIO is "Thermal and External Power Detect". It's uncertain if this
GPIO is set on GPU initialization or only if a change is detected by the
GPU at runtime.

This GPIO can be found in Rankine and Curie and rarely on Tesla GPUs
VBIOS.

Untested, wrote according to documentation.

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