panfrost: Add an helper to update the rasterizer part of a tiler job desc

panfrost: Add an helper to update the rasterizer part of a tiler job desc

That's part of our attempt to make panfrost_emit_for_draw() a bit more
dry and eventually get rid of it by inlining the code in
panfrost_draw_vbo(). This is just one step in this direction.

Note that we get rid of the panfrost_rasterizer.tiler_gl_enables field
along the way, as setting/clearing those bits at draw time instead of
doing when the state is created should make a huge difference. We might
get back to pre-computed VT descs at some point, but let's keep things
simple for now.

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>