freedreno/ir3: fix gpu hang with pre-fs-tex-fetch

freedreno/ir3: fix gpu hang with pre-fs-tex-fetch

For pre-fs-dispatch texture fetch, we need to assign bary_ij to r0.x,
even if it is not used in the shader (ie. only varying use is for tex
coords).  But if, for example, gl_FragCoord is used, it could get
assigned on top of bary_ij, resulting in a GPU hang.

The solution to this is two-fold: (1) the inputs/outputs rework has the
benefit of making RA realize bary_ij is a vec2, even if there are no
split/collect instructions (due to no varying fetches in the shader
itself).  And (2) extend the live ranges of meta:input instructions to
the first non-input, to prevent RA from assigning the same register to
multiple inputs.

Backport note: because of (1) above, a better solution for 19.3 would be
to revert f30c256ec05.

Fixes: f30c256ec05 ("freedreno/ir3: enable pre-fs texture fetch for a6xx")
Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Eric Anholt <eric@anholt.net>