v3d: Move the stores for fixed function VS output reads into NIR.

v3d: Move the stores for fixed function VS output reads into NIR.

This lets us emit the VPM_WRITEs directly from
nir_intrinsic_store_output() (useful once NIR scheduling is in place so
that we can reduce register pressure), and lets future NIR scheduling
schedule the math to generate them.  Even in the meantime, it looks like
this lets NIR DCE some more code and make better decisions.

total instructions in shared programs: 6429246 -> 6412976 (-0.25%)
total threads in shared programs: 153924 -> 153934 (<.01%)
total loops in shared programs: 486 -> 483 (-0.62%)
total uniforms in shared programs: 2385436 -> 2388195 (0.12%)

Acked-by: Ian Romanick <ian.d.romanick@intel.com> (nir)