i965: Set swizzle fields in the VS precompile program key.

i965: Set swizzle fields in the VS precompile program key.

This fixes a regression since 76d1301e8e8e50dc962601a9977bc52148798349:
I began setting SWIZZLE_XYZW for unused sampler units in the actual
program keys, since this matched the FS precompile behavior.  However,
the VS precompile was expecting zero, so that commit made essentially
every vertex shader (even those not using texturing) mismatch and need
to be recompiled.

Setting them in the VS precompile key solves the issue.  It also is an
improvement over our old behavior: previously we guessed that vertex
shaders didn't use any textures at all.  Now we actually look to see if
the VS had any sampler uniforms and guess based on that.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>