drm/xe/multi_queue: preempt primary on queue group suspend

In a multi-queue group only the group's primary queue interfaces with
GuC for scheduling; suspend/resume of secondary queues is handled
internally and is not forwarded to GuC. As a result, suspending a
secondary queue alone (e.g. on its preempt fence signalling) does not
disable the primary's GuC context, so in-flight GPU work of the group
is not actually preempted.

Make a secondary queue suspend/resume like any other queue, driven by
its own xe_guc_exec_queue.suspend_count, and additionally forward the
suspend/resume to the primary so the GPU is actually preempted. The
forward is gated on the secondary's own 0->1 / 1->0 suspend_count
transition, so each group member contributes exactly one suspend
reference to the primary: the primary keeps its GuC context disabled
until every member that suspended it has resumed, including across the
resume-all-queues-each-rebind-cycle behavior. group->suspend_lock makes
the secondary transition and the primary forward atomic, and a member
leaving while still suspended (queue teardown) drops its reference on
the primary.

v2: Add comment about suspend_wait() in drop_suspend()
v3: Do not suspend a secondary if primary is killed,
    wait for primay suspend to complete before drop_suspend()

Assisted-by: Github-Copilot:Claude-opus-4.8
Signed-off-by: Niranjana Vishwanathapura <niranjana.vishwanathapura@intel.com>
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patch.msgid.link/20260713202317.2187787-14-niranjana.vishwanathapura@intel.com

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