i965/gen7: Set up all samplers even if samplers are sparsely used.

i965/gen7: Set up all samplers even if samplers are sparsely used.

In GLSL, sampler indices are allocated contiguously from 0.  But in the
case of ARB_fragment_program (and possibly fixed function), an app that
uses texture 0 and 2 will use sampler indices 0 and 2, so we were only
allocating space for samplers 0 and 1 and setting up sampler 0.  We
would read garbage for sampler 2, resulting in flickering textures and
an angry simulator.

Fixes bad rendering in 0 A.D. and ETQW.  This was fixed for pre-gen7 by
28f4be9eb91b12a2c6b1db6660cca71a98c486ec

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=25201
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=58680
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
NOTE: This is a candidate for stable branches.