st/mesa: inform the driver of framebuffer changes before compute dispatches

st/mesa: inform the driver of framebuffer changes before compute dispatches

Even though compute shaders cannot access the framebuffer, there is a
synchronization issue when a compute dispatch accesses a texture that
was previously bound and drawn to as a framebuffer.

Section 9.3 (Feedback Loops Between Textures and the Framebuffer) of
the OpenGL 4.5 spec rather implicitly clarifies that undefined behavior
results if the texture is still attached to the currently bound
framebuffer. However, the feedback loop is broken when the application
changes the framebuffer binding before a compute dispatch, and the
state tracker needs to let the driver known about this.

Fixes GL45-CTS.compute_shader.pipeline-post-fs on SI family Radeons.

Cc: mesa-stable@lists.freedesktop.org
Signed-off-by: Marek Olšák <marek.olsak@amd.com>