nvc0: add initial support for nve4+ (Kepler) chipsets

nvc0: add initial support for nve4+ (Kepler) chipsets

Most things that work on Fermi should work on Kepler too.

There are a few performance optimizations left to do, like better
placement of texture barriers and adding scheduling data to the
shader instructions (without them, a thread group will be masked
for 32 cycles after each single instruction issue).