drm/panthor: Remove dead code

drm/panthor: Remove dead code

Remove unused function declaration in panthor_gem.h:
- `panthor_gem_prime_import_sg_table()`

Remove duplicate macro definitions:
- `MAX_CSG_PRIO`
- `MIN_CS_PER_CSG`
- `MIN_CSGS`

Signed-off-by: Florent Tomasin <florent.tomasin@arm.com>
Reviewed-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Steven Price <steven.price@arm.com>
Signed-off-by: Steven Price <steven.price@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20250107173310.88329-1-florent.tomasin@arm.com