i965: Fix fp fragment.position handling and enable HW part of ARB_fcc.

i965: Fix fp fragment.position handling and enable HW part of ARB_fcc.

As with swrast, this fixes the default pixel center behavior which was
broken, and implements the previous behavior for integer.  Fixes
piglit fp-arb-fragment-coord-conventions-none.  The extension won't be
exposed until we get the GLSL part implemented.

The DRI1 origin_x/y parts are dropped since they're no longer relevant.