i965: Make setup_vec4_uniform_value and _image_uniform_values take an offset

i965: Make setup_vec4_uniform_value and _image_uniform_values take an offset

This way they don't implicitly increment the uniforms variable and don't
have to be called in-sequence during uniform setup.

Reviewed-by: Francisco Jerez <currojerez@riseup.net>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>