radeonsi: convert the framebuffer state to atom-based

radeonsi: convert the framebuffer state to atom-based

This looks like r600g. The shared Cayman MSAA code is used here.

The real motivation for this is that I need the ability to change values
of color registers after the framebuffer state is set. The PM4 state cannot
be modified easily after it's generated. With this, I can just change
r600_surface::cb_color_xxx and set framebuffer.atom.dirty=true and it's done.

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