etnaviv: Fix point sprite Z,W coordinate replacement

The hardware seems to be only capable of replacing X,Y coordinates of the point, Z,W are left to 0,0. However, the shader program expects W to be a projector and therefore non-zero ; for point sprites W is always 1. Set W to 1 by emitting a shader instruction to satisfy the expectation.

This fixes neverball point sprites (exit cylinder stars) and eglretrace of gl4es pointsprite test:

https://github.com/ptitSeb/gl4es/blob/master/traces/pointsprite.tgz

Note that this depends on the following MR: !9214 (merged)