vc4: Split the coordinate shader to its own vc4_compiled_shader.

vc4: Split the coordinate shader to its own vc4_compiled_shader.

Merging VS and CS into the same struct wasn't winning us anything except
for not allocating a separate BO (but if we want to pack programs into
BOs, we should pack not just those 2 programs together).  What it was
getting us was a bunch of code duplication about hash table lookups and
propagating vc4_compile contents into a vc4_compiled_shader.

I was about to make the situation worse with indirect uniform buffer
access.