drm/panthor: Fix the group priority rotation logic

drm/panthor: Fix the group priority rotation logic

When rotating group priorities, we want the group with the
highest priority to go back to the end of the queue, and all
other active groups to get their priority bumped, otherwise
some groups will never get a chance to run with the highest
priority. This implies moving the rotation itself to
tick_work(), and only dealing with old group ordering in
tick_ctx_insert_old_group().

v2:
- Add R-b
- Fix the commit message

v3:
- Drop the full_tick argument in tick_ctx_init()
- Collect R-b

Fixes: de8548813824 ("drm/panthor: Add the scheduler logical block")
Reviewed-by: Steven Price <steven.price@arm.com>
Reviewed-by: Chia-I Wu <olvaffe@gmail.com>
Link: https://patch.msgid.link/20251128094839.3856402-5-boris.brezillon@collabora.com
Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>