panfrost: Unify barrier+helper handling
These are unified in the hardware, so let's unify them in pan_shader_info. Hoisting this logic to pan_shader.c avoids the need to duplicate this logic for Midgard/Bifrost (RSD packing) and Valhall (SPD packing).
Signed-off-by: Alyssa Rosenzweig alyssa@collabora.com