panfrost: Combine frag_shader_meta_init functions

panfrost: Combine frag_shader_meta_init functions

In order to pack a given structure atomically, we need to group state
together. Since this all affects shader_meta, we'll move it closer
together in the code. This unfortunately creates a "monster" function,
but it's still less code and better organized overall.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Reviewed-by: Tomeu Vizoso <tomeu.vizoso@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6440>