freedreno/ir3: create fragcoord instructions in input block

freedreno/ir3: create fragcoord instructions in input block

This was somehow working to create the instructions in a random block,
and use the value in other blocks, by dumb luck.  But two-pass-RA's
better choice of register assignment causes a couple dEQPs to start
failing without this fix:

dEQP-GLES3.functional.shaders.metamorphic.bubblesort_flag.variant_1
dEQP-GLES3.functional.shaders.metamorphic.bubblesort_flag.variant_2

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3569>