panfrost: Dissociate shader meta patching from the desc emission

panfrost: Dissociate shader meta patching from the desc emission

Right now we emit two shader descriptors for the fragment shader, one
when panfrost_patch_shader_state() is called, and the final one
including both the shader_meta and the blend RT descriptors.
The first generated fragment shader descriptor is never used, since the
second one overrides the postfix.shader pointer.

Let's dissociate the state patching logic from the descriptor emission
so we don't upload descriptors that are never used.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4083>