radeonsi: flush CB after MSAA only when transitioning from CB to textures

radeonsi: flush CB after MSAA only when transitioning from CB to textures

The main flush before texturing is done after the FMASK decompress pass.

CB after MSAA rendering is not flushed in set_framebuffer_state and also
not in memory_barrier if the current color buffer is MSAA. We fully rely
on the FMASK decompress pass for the flushing.

Some CB decompress and resolve passes need an explicit flush before and
after.

Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>