drm/sched: Remove a hole from struct drm_sched_job

We can re-order some struct members and take u32 credits outside of the
pointer sandwich and also for the last_dependency member we can get away
with an unsigned int since for dependency we use xa_limit_32b.

Pahole report before:
        /* size: 160, cachelines: 3, members: 14 */
        /* sum members: 156, holes: 1, sum holes: 4 */
        /* last cacheline: 32 bytes */

And after:
        /* size: 152, cachelines: 3, members: 14 */
        /* last cacheline: 24 bytes */

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Danilo Krummrich <dakr@kernel.org>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Philipp Stanner <phasta@kernel.org>
Acked-by: Danilo Krummrich <dakr@kernel.org>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Philipp Stanner <phasta@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20250221105038.79665-4-tvrtko.ursulin@igalia.com