pan/mdg: Refactor texture op/mode handling

We reduce the op to 4-bits, such that the derivative mode becomes its
own adjacent parameter. This cleans up handling of texture gathers, but
does not affect functionality.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6516>
5 files changed