nouveau: Add support for ARB_sampler_objects

nouveau: Add support for ARB_sampler_objects

ARB_sampler_objects is very simple software only extension to support.  I want
to make it a mandatory extension for Mesa drivers to allow the meta module to
use it.

This patch add support for the extension to nouveau. It is completely untested
search and replace patch, except for flagging the texture state as needing to
be recomputed when a sampler object is present.

Signed-off-by: Pauli Nieminen <pauli.nieminen@linux.intel.com>