nvc0: bind images on compute shaders for Kepler

nvc0: bind images on compute shaders for Kepler

Old surfaces validation code will be removed once images are completely
done for Fermi/Kepler, that explains why I only disable it for now.

This also introduces nvc0_get_surface_dims() which computes correct
dimensions regarding the given target.

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>