anv/pipeline: Put actual pointers in anv_shader_bin

anv/pipeline: Put actual pointers in anv_shader_bin

While we can simply calculate offsets to get to things such as the
prog_data and the key, it's much more user-friendly if there are just
pointers.  Also, it's a bit more fool-proof.

While we're at it, we rework the pipeline cache API to use the
brw_stage_prog_data type directly.

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98012
Reviewed-by: Topi Pohjolainen <topi.pohjolainen@intel.com>
Reviewed-by: Timothy Arceri <timothy.arceri@collabora.com>
Cc: "13.0" <mesa-stable@lists.freedesktop.org>