radeonsi: update dirty_level_mask only when flushing or unbinding framebuffer

radeonsi: update dirty_level_mask only when flushing or unbinding framebuffer

This fixes corruption with bindless textures in Dawn Of War 3.

The do_update_surf_dirtiness mechanism was complicated and dirty_level_mask
was only updated after the first draw call. The problem is bindless textures
are checked for decompression every draw call and we would only decompress
after the first draw call. The solution is to set dirtiness after the last
draw call to the framebuffer, so the (unconditional) decompression of
bindless textures happens at the right time.

Cc: 17.2 <mesa-stable@lists.freedesktop.org>
Tested-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>