panfrost: Specialize compute vs frag shader init

panfrost: Specialize compute vs frag shader init

In exchange for a bit of code duplication, we can streamline both
routines. A huge amount of the descriptor is unused for non-fragment
shaders, and even some of the parts that are used appear to have varying
meanings. Given we want to emit the descriptors atomically, this seems
like a reasonable tradeoff.

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>