i965: Split the gen4 and gen5 sampler handling apart.

i965: Split the gen4 and gen5 sampler handling apart.

Trying to track the insanity of the different argument layouts for
normal/shadow crossed with normal/lod/bias one generation at a time is
enough.

Fixes: glsl1-texture2D() with bias.
(first test passing in this code that doesn't pass without it!)