i965: Make Gen4-5 push constants call _mesa_load_state_parameters too.

i965: Make Gen4-5 push constants call _mesa_load_state_parameters too.

In commit 5e37a2a4a8a, I made the pull constant code stop calling
_mesa_load_state_parameters() when there were no pull parameters.

This worked fine on Gen6+ because the push constant code also called
it if there were any push constants.  However, the Gen4-5 push constant
code wasn't doing this.  This patch makes it do so, like the Gen6+ code.

A better long term solution would be to make core Mesa just handle this
for us when necessary.

Fixes around 8766 Piglit tests on Ironlake, and probably Gen4 as well.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>