Instead of all shaders being stored in a single BO, have each shader in
its own.

This removes the need for a 16MB allocation per context, and allows us
to place transient blend shaders in BOs marked as executable (before
they were allocated in the transient pool, which shouldn't be
executable).

v2: - Store compiled blend shaders in a malloc'ed buffer, to avoid
      reading from GPU-accessible memory when patching (Alyssa).
    - Free struct panfrost_blend_shader (Alyssa).
    - Give the job a reference to regular shaders when emitting
      (Alyssa).

v3: - Split out the allocation flags change (Rob).

Signed-off-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>