drm/gk20a/fb: fix setting of large page size bit

Commit "ltc/gf100-: fix cbc issues on certain boards" moved the setting
of the large page size bit from bar/nvc0 to fb/nvc0. GK20A uses its own
FB device and the change was thus not applied to it - fix this.

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