drm/sched: Re-order struct drm_sched_rq members for clarity

Current kerneldoc for struct drm_sched_rq incompletely documents what
fields are protected by the lock.

This is not good because it is misleading.

Lets fix it by listing all the elements which are protected by the lock.

While at it, lets also re-order the members so all protected by the lock
are in a single group.

v2:
 * Refer variables by kerneldoc syntax, more verbose commit text. (Philipp)

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Luben Tuikov <ltuikov89@gmail.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: Philipp Stanner <pstanner@redhat.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Philipp Stanner <pstanner@redhat.com>
Signed-off-by: Philipp Stanner <pstanner@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20241016122013.7857-4-tursulin@igalia.com