drm/nouveau/fb/gf100-: declare constants as unsigned long long.

Explicitly declare constants as unsigned long long to address the
following sparse warnings:
warning: constant is so big it is long

v2: convert to unsigned long long for compatibility with 32-bit
architectures.

Signed-off-by: Wambui Karuga <wambui.karugax@gmail.com>
Suggested by: lia Mirkin <imirkin@alum.mit.edu>
Signed-off-by: Ben Skeggs <bskeggs@redhat.com>