panfrost: Prepare shader_meta descriptors at emission time

panfrost: Prepare shader_meta descriptors at emission time

This way we avoid potential state leaks and keep the shader_meta
initialization in once place. The time spent preparing the shader
descriptors should be negligible compared to the time spent pushing
those descriptors to the transient buffer (remember we are writing to
non-cacheable memory here).

Note that we might get back to some sort of shader_meta descriptor
caching at some point if that proves necessary, but now we have those
panfrost_frag_meta_xxx_update() helpers now where xxx maps directly to
a CSO bind, which should ease desc template updates.

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>