panvk: Emit fragment RSDs even with no shader

panvk: Emit fragment RSDs even with no shader

In Vulkan, it's possible to create a pipeline with no fragment shader that's
still expected to rasterize. This is useful for depth/stencil side effects, and
is closely related to the "fragment shader required" optimization we do in the
GLES driver. Refactor the RSD emit code to handle this case.

Fixes dEQP-VK.pipeline.stencil.nocolor.*

Signed-off-by: Alyssa Rosenzweig <alyssa@collabora.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16204>