drm/nouveau/volt: switch to instanced constructor

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

drm/nouveau/volt/gm20b: add support for vmin parameter

Chips may be characterized for a minimum voltage. Support this extra
parameter and select the appropriate minimum voltage for the detected
GPU speedo.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/volt/gk20a: rename constructor

Strip the _ prefix off the gk20a volt constructor.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/volt/gk20a: make unused public functions static

Nobody else is using these, so make them private.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/volt/gk20a: split constructor

Split the constructor function so we can reuse the same logic in other
chips.

Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>

drm/nouveau/volt/gk20a: share reusable members & functions

The CVB calculation and voltage setting functions can be reused for the
future chips. So move the declaration to gk20a.h.

Signed-off-by: Vince Hsu <vinceh@nvidia.com>
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>