anv/pipeline: Whack nir->num_uniforms to MAX_PUSH_CONSTANT_SIZE

anv/pipeline: Whack nir->num_uniforms to MAX_PUSH_CONSTANT_SIZE

This way any image uniforms end up having locations higher than
MAX_PUSH_CONSTANT_SIZE.  There's no bug here at the moment, but this
consistency will make the next commit easier.  Also, because
nir_apply_pipeline_layout properly increments nir->num_uniforms when
it expands the param array, we no longer need to stomp it to match
prog_data::nr_params because it already does.

Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>