radeonsi: move DB_SHADER_CONTROL into db_render_state

radeonsi: move DB_SHADER_CONTROL into db_render_state

I will need this for fixing sample shading with 1 sample.

The good news is that all shader pm4 states no longer use the current context
state, so we can generate the pm4 states outside of draw_vbo if needed.

Reviewed-by: Michel Dänzer <michel.daenzer@amd.com>