freedreno/ir3: simplify creating sysval inputs

freedreno/ir3: simplify creating sysval inputs

In almost all places, the add_sysval_input() is paired directly with a
create_input().  (The one exception is frag shader ij bary coord, and
this exception will go away in a later patch.)

So go ahead and clean this up before reworking input/output handling.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Reviewed-by: Kristian H. Kristensen <hoegsberg@google.com>
Reviewed-by: Eric Anholt <eric@anholt.net>