freedreno/a3xx+a4xx: fix for stk binning pass hang

freedreno/a3xx+a4xx: fix for stk binning pass hang

We'd end up in a state where shader uses no inputs, yet num_elements is
greater than zero.  Triggered by a TF vertex shader which did:

  gl_Position = vec4(0.0, 0.0, 0.0, 0.0);

resulting in a binning pass variant with no inputs.

Includes equiv fix in a4xx, even though we don't have binning-pass
enabled yet on a4xx.

Signed-off-by: Rob Clark <robclark@freedesktop.org>